Well, that depends. Are you talking about them leaving over abortion? Why would they leave now when they never have before?
If they're not leaving over abortion specifically but over the whole socon vs. libcon thing, Romney will be an acceptable canddate to them, and so would Huckabee once they get a gander at his record. I hate that that's where we might end up, but I only see fracture if Rudy's the nominee, and perhaps not even then.
Let me try to answer that, because it's a very important question.
There are a lot of people who would vote in a referendum question, once Roe v. Wade is overturned, to severely restrict but not ban abortion. This is the majority position in the country, I think, or it could become so.
Most of those people understand that abortion will never be "banned" or "outlawed", at least not until the American libido is restored to what it was in, say, 1950. That's a bad thing (at least I think it is), but it's the truth.
Now, we come to the GOP on abortion. I understand, and I think most people who have consistently voted Republican since 1980, understand the platform to express a wish, or a desire, for an end to abortion. The language in the platform is not an action plan (or, if it is, is is the most weak and ineffectual action plan in history). George W. Bush said as much when he said that nothing could happen until "America's heart" changed on the subject. FDT recently said something quite similar.
But there is a faction of post-1980 GOP voters who believe that their political action WILL have concrete, direct results such as amending the constitution or passing laws against abortion. This faction is becoming increasingly frustrated because, despite their loyalty and their efforts, NOTHING IS HAPPENING.
So now, they want more than the meaningless platform. They want a candidate who, when he says he is pro-life, a) isn't lying, and b) means to do something about it, beyond appointing USSC justices with a 50-50 chance of being Scalia or Souter.
For these people, a guy like Hunter or Huckabee is the real deal.
But the voters, mired in ambivalence about abortion, are not about to elect a man who will really act against it, rather than engage in the charade of ending his pro-life work by signing the platform.
A real anti-abortion nominee is another Goldwater, and will make 2008 another 1964. You know it, and I know it.
Those who want such a candidate say "Good! Tear it all down, and the rebuilding can start. Then, 2028 (or whenever) can be 1980 all over again"
For myself, I don't think the nation can survive another 1964. Besides LBJ, we got the most radical Congress in history, and a spate of America-destroying legislation unlikely ever to be reversed.
If the Democrat nominee brings in 68 senators and 295 representatives, like LBJ did, what they will do is beyond imagining.
The reason the 30% "Rudyites" haven't left over abortion before this is that they AREN'T "abortionists" and "baby-killers". They're content with the platform language, just as long as nobody running on the platform does anything about it.