While I am sure he had some idea churning in his head about how the ship got more power - even ZPMs would have been depleted by now, and he knows that ship predates that technology by many thousands of years if not longer - I am not sure if he was 100% sure. Seriously, I think we are ignoring that Rush is a much deeper character than he so far has presented. He is extremely intelligent, emotionally handicapped, socially unstable in a manner that would make Rodney look absolutely normal, but yet, I feel there is something more to him. While he has been "right" quite often, I think they are setting him up to be the anti-Carter/anti-Rodney. No matter what, when one of those two suggested something in SG1/SGA we went with it. Here, we aren't so easy to trust Rush, and someday that may really bite us in the ass. I think that is the way TPTB want it.
So IMHO, I think that, yeah he had an inkling that something would happen to save their lives, but on the other hand, I don't think he was willing to bet every single one of their lives on one of his wild and crazy ideas (again).
Of course, I could be wrong and he could just be a sadist who wanted to see the others put through the proverbial wringer and possibly hoping that some of the crazier nut jobs (like the IOA woman) would be "lost", but that would mean his character is less deep than I know him to be.