OK here's a dream scenario for ya...
..McCain wins...but finds he must drop out (leave that to your imagination)
Palin assumes Presidency and names Hunter as VP :)
McCain will never drop out on his own accord. Hes too stubborn for that. He may have to for health reasons before his term was out but I don’t wish that for anyone. A few times I have entertained the notion that McCain plans on doing that after he gets elected so we can get Sarah Palin as president but thats too farfetched.