David Brooks predicts what will happen after the Affordable Care Act melts down:

When the crisis comes, Democrats will face an interesting choice — to patch the Obama system or try to replace it with something bigger. The administration may want a patch, but by a ratio of nearly 2 to 1, according to a CNN poll, Democratic voters would prefer a more ambitious law. Liberals could logically say that the mistake was trying to create a hybrid system, rather than moving straight to a single-payer one.
Republicans are going to have to move beyond their current “Repeal!” posture and cohere behind a positive alternative. One approach, which Tyler Cowen of George Mason University has written about, is to allow more state experimentation. Another approach, championed by Capretta, Yuval Levin of National Affairs and Thomas P. Miller of the American Enterprise Institute, revolves around the words “defined contribution.”
Under this approach, Republicans would say that the federal government has a role in subsidizing health insurance — a generous role, but not unlimited. The government would provide needy citizens with a predefined amount of money to spend on insurance and allow them to shop in a transparent, regulated, but not micromanaged marketplace.

Ezra Klein does a good job of explaining why the PPACA will not, in fact, melt down at all. He does concede that some parts will no doubt work less well than expected (and others probably better.) 

But the key point is that, if the PPACA does encounter problems and require changes, we will now be starting from a totally different position. The most serious and elemental fight of the entire issue was over whether the uninsured should be covered at all. Many conservatives made a principled argument that being able to obtain health insurance is a personal responsibility, and if people can't do it on their own, those virtuous enough to obtain it shouldn't have to have their money confiscated to subsidize the losers. Other conservatives conceded that, in theory, covering the uninsured might be nice, but they opposed any use of resources at all that would be needed to pay for it. (Want to cut Medicare waste and use the savings to cover the uninsured? No dice -- use it to reduce the deficit instead.)

Basically throughout the entire course of American history, conservatives in political power have shown zero interest in reforming American health care and/or finding a way to cover the uninsured. If they want to get into the game and reform health care now, terrific. The good news is that we're now starting in a world in which having 50 million Americans go without coverage is no longer a given. Conservatives may change some things about the PPACA, but they won't be able to change that.