I seriously doubt that McCain will win the primaries. The base doesn't trust him. He's pro gun control, anti-free speech, weakly pro-life, and has some corruption problems in his past.
I'd hold my nose and vote for him in the general in that unlikely event, but he would lose. Much of the base would stay home or peel off.
It looks to me as if the alternative to McCain is Guiliani who has been traveling extensively raising money for Republicans and collecting IOUs. I don't believe any other candidate polls in double figures consistently.
What is termed the "base" around FR is a small collection of ideologues who have no one capable of winning the nomination. The biggest issue for the GOP is controlling their temper tantrums when whoever they favor goes down in flames and they will.