I don’t think McCain will win simply because he is doing his very best to insure that conservatives stay home this fall.
Today the national security issue including the overseas WOT and the proper surveillance techniques here is of primary importance. It is in this venue I believe McCain is head and shoulders above anyone on the left and most especially the empty suit.
That said, what ever hard line Conservatives McCain loses (and I don't think in the end it will be near as many as you think, he will more then make up for by grabs from the center and right.