Can he not switch to the Dems in this case
McCain sort of promised Harry Reid and other Dem leaders that he would vote with Dem caucus if he wins. This saves him from their withering fire. But if they start to push him around, he can always switch. He could switch anyway, but would be seen as a turncoat (ala Jumping Jim Jeffords). He might also incur the wrath of Connecticut voters, but he will probably not want to run again anyway. Next to Zell Miller, Smokin' Joe is my favorite "Dem" Senator.
Of course, and he may very well do just that.
But, there's one thing that Joe has that 90 % of today's RATs don't have and that's patriotism and integrity. Those two qualities alone may keep him as an "I"...and I do think he is going to win.