Now that we're past the constitutional question on the ACA, we've moved on to "Can it survive a Romney presidency?". Most people think the answer is "Yes because Democrats would filibuster the repeal attempt." but Matthew Yglesias reminds us (as if we needed it) that the filibuster rules the Democrats were operating under were entirely self-imposed:

What I think this misses is that in the real world there are very few practical constraints on reconciliation. The operational issue the Obama administration had with reconciliation is that there were a clutch of 10-15 Democratic Senators who preferred a 60-vote Senate because it put shifted the pivot point and put policy outcomes closer to their personal ideal points. It was those Senators who raised a lot of niggling objections about reconciliation rules.

The GOP is more ideologically unified and more focused on advancing a broad conception of the national interest rather than parochial concerns of individual legislators. Here's how they handled the reconciliation process last time Democrats attempted to filibuster a major legislative priority:

The senate parliamentarian serves as arbiter of the Senate's rules. Although the vote of 60 senators can overrule the parliamentarian's decision, that seldom happens. What drew Lott's ire were the parliamentarian's decisions that made it easier for Democrats to stall the president's tax and budget bills. (Senate rules generally prevent filibusters on budget and tax bills. And the GOP leadership wanted those rules interpreted as broadly as possible. But Dove didn't always comply. Earlier he ruled that only one tax bill a year could be immune to a filibuster. And more recently, he ruled that a disaster relief set aside also wouldn't be getting the no-filibuster free ride.) Desiring more accommodating decisions, he fired Dove.

That is how you get things done in Washington when you want to get things done.