Senators Tom Cotton, Susan Collins, John McCain, and Lamar Alexander are four Republican senators who have expressed concern about repealing Obamacare without offering a plan to replace it. That's more than their 52-48 margin, and several other more moderate Republican -- and all 48 Democrats -- would probably join them.
Of course, being wary about it does not mean that they would vote against it. And there does seem to be intense political pressure from the leaders to repeal it right away. But that, too, is telling. If they think it's more important to do it immediately, rather than carefully, then they're going to screw it up, sooner or later.