If the distance between Williams and Ferrari remains the same for next year, no Williams driver will challenge Ferrari.
Button next year shouldn't even worry about Ferrari. He should have his eyes on Webber and understand that Webber is the first person he has to care about defeating. Beating Ferrari and Schumacher would then only be a consequence or something to be acheived later. But he must have it clear that Webber is the primary target. And, from what I've seen of Webber so far, it seems as if he'll do all he can, including those mind games and not so fair teamwork, to beat Button or anyone 'til the very end of his career, so Button better be smart.