This one isn't all that complicated in terms of its political impact.
If the GOP can't pass a new Health Care bill, even an imperfect one, that the Dems are going to take back the Senate and perhaps the House...and we'll be getting single payer Health Care. This isn't a matter of choosing the lesser of two evils for these conservatives, its the difference between "lightning and a lightning bug" (Mark Twain quote).
If you can't score a touchdown, take the field goal and try again on the next drive...this is a matter of tactics, not principle. We all understand that "we" want a fully free market solution in the end...this is about how do we get to that. Killing the whole bill moves us irreparably away from that goal, finding a way to get it through moves us...albeit incrementally...towards the goal.