Romney is looking at 2012 no matter who wins. McCain isn't going to run for a 2nd term, and there's no way they'll let Palin run for the top spot. (I don't think)
Has he said that he won't run for a second term?
And yeah, as someone at the American Conservative Magazine argued, Palin isn't the future of the GOP. If that scenario you described happens, Romney/Pawlenty/Huckabee will fight in a brutal steel cage match, with Palin perhaps the first to go.
