That seems to be the big question. Here’s Victor Davis Hanson’s take:

If McCain gets the nomination, I would have to believe that the Republican sit-out would only last midsummer until they could not take Sen. Clinton no more, and thus like Lancelot at Camlan belatedly enter the fray.

But then you have someone like Coulter who says she’ll campaign for Hillary if McCain it the nominee (go watch the video clip and see how happy Colmes is with Coulter). And you have Michelle Malkin hinting at not voting for him.
But some Christian conservatives seem to be embracing him:

Tony Perkins, a prominent Christian conservative who has often denounced Mr. McCain, is warming up to him, too.
“I have no residual issue with John McCain,” Mr. Perkins said, adding that the senator needed “to better communicate” his convictions on social issues.
Richard Land, an official of the Southern Baptist Convention and a longtime critic of Mr. McCain, agreed, saying, “He is strongly pro-life.”
“When I hear Rush Limbaugh say that a McCain nomination would destroy the Republican Party,” Dr. Land added, “what I want to say to Rush is, ‘You need to get out of the studio more and talk to real people.’ ”

BTW, I’m surprised that someone who supports federal funding of embryonic stem cell research and abortions for victims of rape and incest (I guess its OK to kill a baby in that case) would be considered “strongly pro-life.”
And Hewitt is going to do what he can to rehabilitate McCain for the November vote and has started early by having a very convincing McCain supporter, Bruce Herschensohn on for a number of segments on his radio show last night (MP3 file here and here).
As an anyone but McCain voter, I guess I should come to grips with the fact that doesn’t extend to Clinton because I couldn’t in good conscience vote the Clintons back into the White House. So, I will be voting for McCain if it comes to that in November. I don’t agree with Coulter that McCain is worse on the war than Clinton would be. She is reported to have an animosity towards the military so how could I support inflicting her on the military after they sacrifice so much to serve?
Update: I just published this and then I read this and I’m thinking, “Way to reach out to the conservatives, dude.” If they make it impossible for me, I will vote for whatever 3rd party is the most conservative.