Short version: OMG, I cannot believe there is even the slightest risk of this show being cancelled. It's so awesome. I really haven't had this experience of being this invested in a US show at the same time as its fate is genuinely in the balance before. The feeling of powerlessness isn't much fun, actually.
The long version under the cut has spoilers for pretty much everything Terminator-ish ever, including SCC 2x22; it is mostly about time travel and a bit about Obvious Religious Imagery, because those are what I'm qualified to talk about as a Doctor Who fan.
Any episode that starts with the gorgeous tones of Unexpected Josh Malina is automatic win (I think he does believe Sarah, incidentally, in that bit later on; but that may be the gorgeous tones influencing me), but Born to Run was very win indeed. It laid some of the themes (especially the religious stuff) on a bit thick -- if your main character's initials are JC and he's going to save humanity from "the devil" we don't actually need someone saying that his mum thinks he's the messiah (missed opportunity in that "I told you not to come back for me" scene in the car after the jailbreak for a Life of Brian reference, I think) -- but there was some wonderfully subtle stuff in there about the AIs, particularly John Henry apparently displaying some sort of Penrose-style "quantum" dependence on particular hardware.
I really don't know what to make of the ending. It raises so many new questions that it leaves almost completely open and I sort of MUST KNOW. But in the absence of knowledge, I will make do with spec. Long, rambly spec. Hit "back" now, srsly.
[I should probably start by pointing out that I only came on board properly at the beginning of S2. So there is doubtless oodles of spec and uncertainty here that if I had seen some particular point of some S1 episode would be abundantly clear.]
There are (it seems to me) two classic models of sfnal time travel, both based around possible answers to the hoary old Grandfather Paradox.
The first is the entirely deterministic model, where everything is as it was always meant to be and any attempt to change the past will turn out to have been part of events all along. This is your "--All You Zombies--" version, or in Richard & Judy terms, The Time Traveller's Wife. The original Terminator film arguably fits this pattern, with Kyle turning out to be John's father a big "LOL irony" to give a bit of depth to what's basically a superior action flick. But T2 seems to rule it out for the movie canon, especially with the "no fate" line (according to Wikipedia, it was supposed to end with a "yay, we stopped J-Day" coda which ... well, I'm very glad it didn't, both in terms of the fact that we got SCC and for the sake of T2 not undermining itself), and SCC repeatedly explicitly shows the malleability of the timeline -- Richard Schiff's character in that episode he was in (obv if S3 does happen, we have to have Rob Lowe for the complete set of communications bullpen types), Jesse not being Derek's Jesse, and most notably that one where Cameron researches the terminator sent too far back in time, who had to take active steps to preserve the timeline he wanted to be in to be able to assassinate the Governor of California (which, incidentally, is my candidate for best. meta joke. ever.).
A malleable timeline, of course, means that you can come from a future that then stops existing because of your intervention in its past. This definitely seems to be SCC's vision of things, though it's possible they have a more complicated idea. Chris Claremont's X-Men stuff ended up with a model where the annulled timelines still exist out there somehow, but are no longer the future of the main 'verse. You could also go for something with a handwavy "quantum mechanical" aspect, such as Many Worlds theory with added complications for time travel, or some sort of "sum over histories" approach, where the existence of time-travel allows unlikely paths that ought to cancel out to instead reinforce one another or something. (Another possibility is that we're still in the predestination paradox model, just across multiple universes -- for all we know, SCC might end with John sending Kyle to protect Sarah in 1984.)
The ultimate conclusion of a malleable-timeline model is that every single use of a time machine changes the world. Even without the godlike powers of a Time Lord, all the real power is in the hands of time travellers (assuming they can bring their plans to fruition in the past, pace Jesse), and everything else is a distraction. I can't help thinking of future-John's "chess game with Skynet" (as described by the guy on the Jimmy Carter whose name I've forgotten) as a four-dimensional one. A big attraction of this model is that it allows us to reconcile seemingly very divergent bits of the canon. Rise of the Machines can be seen as coming from a point where Skynet is on the attack in the 4-d chess game, when sending a single knackered old Terminator just to try and preserve John through Judgement Day is a Hail Mary (I am mixing my sports metaphors, it must be all the Sorkin actors). By the time SCC rolls around, things seem to be going much better for humanity -- Judgement Day has been postponed considerably (for storytelling purposes, obviously, but still) and there's "metal on every base", which to me suggests that somewhere in the developmental path that leads to Terminators something happened to make them much easier to subvert/reprogram/what have you -- possibly because of Sarah and John's continued attempts to prevent Skynet's creation in the past? It also seems that time travel itself is increasingly common -- the first film presents sending Kyle into the past as a major operation, whereas everybody and their dog seems to be able to jump back in SCC's future.
At some point, something someone did created a major change to the timeline that brought about this more favourable state of affairs, possibly a whole series of several steps bringing things to a better state of affairs. I'm actually very tempted to write fic of the John of the Rise of the Machines future realising that he has to retro-annul his entire relationship with Kate for the greater good; they only met in that rather desperate version of events, etc. etc. And given that the only safe place from being annulled is the past, it seems to me that one answer to the point Sarah made to Cameron in ... er, whichever fairly recent episode it was ... about "why did future-John send you away?" might be that he cared about her enough [whatever his exact relationship with her is, which I'm sure we can speculate about until the cows come home] to want to preserve her existence through some major game-changing time travel gambit -- like, say, shifting everybody into the future. The very setup of SCC opens up a whole set of new possible timelines. Maybe future-John sent Cameron to do that not because she was necessarily the best qualified or whatever but so that she wouldn't be retconned out of existence by the very act of doing it.
A malleable timeline has a giant bit of fridge logic attached, in the form of why Skynet doesn't just send a Terminator unit back to 64 million BC with instructions to build a giant world-girdling computer in which it can instantiate itself and inhibit the development of humanity entirely whilst having more processor cycles than it could ever dream of to do whatever it is Skynet actually wants to do with itself once it's won. Given the "John Henry only exists as this hardware and this software" stuff, it may be that Skynet feels that the AI in the past created by such a process would not be "itself". (The fact that Skynet apparently can't time travel, given that there is such a thing as "living metal", raises the question of whether Skynet is really alive or not, though it may just be unwilling. The whole only-living-things restriction is obviously mainly a clever restriction from the storytelling point of view, but it's very interesting in terms of the time travel, and to me hints towards something based on the Copenhagen Interpretation, all about "observers" and such.)
So, there's a constantly shifting timeline, but -- up until the end of 2x22 -- it seems to have some fixed points -- Skynet and John Connor both exist, and somewhere between the present day and the 2020s Judgement Day happens. The multiplicity of different versions of them seem to be engaged in a minor time war, which is going quite well for John at the moment. But things are changing, with other factions getting in on the act -- Jesse's attempt to influence John away from his reliance on the machines, and whatever game Weaver's playing on the metal side of the equation. It somehow feels like we're possibly heading towards an endgame. This may be partly my own sense that narratively, it'd be hugely unsatisfying for SCC to end with the revelation that everything we've seen was just another minor gambit in the time war, and the final version is going to be radically different again. But the fact that we've just had another massively game-changing forward-time-travel event -- there is no future-John any more! -- seems to hint to me that things are coming to a head
In terms of what that endgame might be, I think it becomes worth thinking about the clunking religious stuff. The messianic overtones are obvious even without the overdose of them in the most recent episode -- the first film is essentially the Annunciation if Gabriel had to protect Mary from a demon sent to kill her -- though it's worth pointing out that Skynet's apparent creative ability makes it a Manichean rather than conventionally Christian universe, and of course it's very tempting, especially in our post-Dan-Brown world, to cast Cameron as Mary Magdalene -- very close to John but reviled by others around him. It's a pity that that episode went so unsubtle on this stuff, because I was quite enjoying the vague trinity of different Johns -- the way we never see future-John makes him very much the remote God-the-father figure (the Annunciation parallels are inexact, of course, but he did send Kyle), the Emperor-across-the-sea in Narnia terms; "our" John is clearly John-the-son, and it's the focus on who his mother is, rather than his father, that makes Terminator interesting in these respects; and then there's the "John Connor" the future humans talk about reverently, who's a bit Holy-Spirit-ish in terms of being inspiration and so on.
Anyway, the point I was aiming towards (before I got sidetracked by dumping every other thought I've ever had about the religious aspects into one paragraph) is that the end of the other JC's story is, of course, that he dies and then comes back. It's very possible to see a time travel version of this where John himself goes further back in the past than we generally see (the library research episode proves that this is possible) and does something that irrevocably averts Skynet's creation, but in such a way that his own birth is retconned away -- sacrificing himself to save humanity from the consequences of its meddling-with-things-man-was-not-meant-t
In some ways, though, I doubt the showrunners would jump this way. A lot of SCC, and certainly the stuff I find most fascinating to watch, though it feels very hard to write about sensibly, is all this fantastically interesting stuff with the questions around AI. Both Cameron and John Henry are used to interrogate what the difference is between human and machine consciousness, if there is any really, and it's all wonderful stuff that doesn't seem to lend itself to an ending that comes down on the side of "machines soulless and bad, version of history with none of them in good" -- Sarah and especially Derek and Jesse's feelings along such lines are increasingly presented as prejudice. The existence of John Henry, and especially the presence of him (and/or Cameron in his body, or whatever the hell's going on) in the future (incidentally, if there is still Cameron in there I shall LOL and LOL given the whole story of Dekker's leaving Heroes), and especially especially the explicit parallelism Weaver makes between John Henry as her son and John Connor as Sarah's, seem to be suggesting something that's more about healing the divide and/or realising that the two things that seemed opposed were in fact not.
So in conclusion: I basically have no bloody clue what they're going to do next. And I want to know. So pls don't cancel this show, Fox? Kthxbai.