I don't think the rules of paradox speak against postponement as long as all the players are the same.
Consider for a moment that, without time travel, the events that played out in the second and third films had no bearing on whether or not judgement day occurred. That is to say, the arrival of the terminators didn't really affect anything that probably wouldn't have happened in the first place without their participation--aside from the T800 postponing Skynet and the lady terminator later speeding up its launch.
It stands to reason that, had they never shown up, Connor still would have met Brewster, Skynet would launch later on and they'd still survive to head the revolution.
I think Scorpius got it right: time is more elastic than it is brittle--at least from a Hollywood standpoint.
