I don't think that the GOP will float McCain. If he runs, the door will be open for the Dims to take the presidency barring a good 3PC.
I have a hard time believing that McCain will be reelected in AZ in '10. In fact, I'd guess that if he were running this fall, he'd lose.
I'm still surprised he won last time. But, there are a lot of people who do not follow politics who think McCain is some sort of hero because the media says so. I have moderate in-laws who think he's great. When I told my sister-in-law his stance on illegals before these bills came out, she said he probably was just more compassionate because he had been prisoner in a foreign country.
If McCain runs again for the Senate, there had better be someone ready to run against him in the primary.