If McCain picked Duncan Hunter as VP, I would be inclined to vote for him sine vomito but, if he picks somebody like Goober Grahamnesty, forget it. It's really unfortunate that the primary process (and by extension the modern GOP) had been set up in such a way that someone like McCain was guaranteed.
On the bright side, if McCain wins, a college freshman in 2009 will be able to play drinking games with the phrase "My Friends" until graduation.
What other choice has he? An outright Democrat?
If he had a conservative veep, it wouldn't take 4 years for a situation to develop where the veep must either turn on McCain or publicly betray his own conservative principles.
Thus, it's doubtful McCain would select someone with integrity to be his veep, when he can't depend on that man to support him in his inevitable McCainical endeavors*. And in the unlikely event McCain does pick a conservative, I'd immediately get skeptical of that person.
*Such as? Such as subverting the First Amendment and granting citizenship and freebies to all-God's-children.