>>>The usual line of succession would not apply...
Either McCain/Palin would win by defaqult or a whole new election would have to be held...McCain/Palin V Clinton/Whomever
Of course that opens up a whole other can of worms as to whether John McCain, born on Panamanian soil, is a natural born citizen. While a minority, there are those that say one must be born on US soil to be a NBC. Since NBC is not defined by the Constitution, that question could possibly end up in the hands of the Supreme Court.
It goes to jurisdiction. He was born on a US occupied military base and hence US soil. Both parents were US citizens. McLame is a natural born US citizen.