The reason why Palin was chosen, was precisely because she had defeated Frank Murkowski and had then gone after the oil companies on some state level issues.
That is NOT why Palin was chosen. It probably didn't hurt, but it was definitely not the main reason she was chosen.
Anyway, this match-up depends largely on whether the Edwards affair still goes down as it did and is exposed as it was, and also possibly if the Access Hollywood tape is exposed early too. If both Democratic candidates crash and burn in sex scandals, McCain could pull the upset potentially, though the fundamentals obviously still favor Trump.
By the way, I would vote for McCain in this election, especially with hindsight, but possibly even without it. Even when he was just the host of The Apprentice, I've never liked Donald Trump. Always saw him as a sleazy scumbag. I would be dismayed if my party nominated him, and would trust that at least McCain was competent and patriotic enough for the job. The pick of Murkowski for VP wouldn't hurt either, as it would certainly suggest he would be no far right culture warrior as president.