They would both end up Goldwater ‘64 / Dole ‘96.
RINOs be damned, electability matters.
How electable is McCain? He has ticked off so many people in his own party that he'll lose lots of votes because of it, and he's not exactly going to be the darling of the media or the lefties with his pro-Iraq War stance. Being a maverick has its advantages (mainly free publicity, invitations to more parties, etc.), but making you more electable for national office isn't one of them.