^But Back to the Future & The Terminator follow 2 different theories of time travel. Back to the Future is a grandfather paradox. The Terminator is a predestination paradox. Marty McFly was able to go back in time and threaten his own existence by changing the timeline. The T-800 couldn't change jack shit. Anything it did in the past would create, not alter, the present that it came from.
Now, if we were to apply the timetravel logic of The Terminator to Back to the Future, Part II, then Back to the Future, Part II would have played out very differently. In that case, when Marty & Doc returned to 1985, it would have been the 1985 that they recognized, not the bizarro world where Biff is a millionaire, because, in 1985, Marty & Doc in the future had already gone back to 1955 to prevent Biff from giving the sports almanac to himself. They also could have gone back to the same 2015 that they recognized, although they would be incapable of doing anything to stop Biff from stealing the time machine and going back into the past because it had already happened.
The real question RE The Terminator is, if changing the past is impossible, then why did Skynet bother to build a time machine in the first place? I figure it's because it's impossible to know which kind of time travel logic you're dealing with until you actually try it. Until then, it's just guessing. Skynet was hoping that they were dealing with Back to the Future timetravel logic but turned out to be wrong.