There is nothing wrong with Congress modifying a program already created by a bill they have already passed. They would do this to correct problems with what they have already created. And, like all such large governmental efforts (or large private efforts for that matter), there WILL be problems. This will be the legitimate duty of Congress with the ACA, just as it has always been with any other program!
But, to just totally shut such a program down that potentially has so much benefit to so many Americans, and then to have to start the whole legislative process over again, would be just unconscionable for Congress. If this is too hard for some in Congress (the tea party types for instance), then perhaps in 2014 it would be time for their actual employer in the people of the United States to consider their voluntary retirement, and elect more reasonable representatives. Representatives that would be more willing to actually work for all of the people of the US, and not just those in the financial end of the Health Care industry!!!
Or, am I being too hopeful here?