I think a lot of Republicans (and Democrats, too) believe that it would be impossible to repeal and replace ObamaCare unless they controlled both houses of Congress and could retake the presidency in 2017. However, I believe there is another scenario that could seal ObamaCare's fate in 2015.
If (and that is a big "if") the Democrats receive a similar shellacking in 2014 as was seen in 2010, and they lose control of the Senate and see even more losses of seats in the House, a number of Senate Democrats may possibly be willing to side with Republicans in repealing ObamaCare. Enough, even, to override an Obama veto. I can say this with confidence because no Democrat is going to be willing to lose another sweeping election because of their continued support of ObamaCare.
The only way Republicans can pull this off is to offer a bill that, in the very first paragraph, repeals or supersedes ObamaCare and, then, goes on to outline a new reform of heath care. One that would have clear public acceptance over the current law and one that, at the very least, is somewhat acceptable to the Democrats.
The biggest hangup in doing this will be the Republican's insistence on tort reform. Because trial lawyers are such big donors to the Democrats, it will be very difficult for any of them to vote for a bill that would harm that critical donor base. In fact, right now, ObamaCare, with all of its legislative facets, is a potential gold mine for trial lawyers if health care providers and insurance companies fail to comply with any parts of the law; leading to both Federal and civil lawsuits being filed. While tort reform would definitely benefit the country as a whole by lowering health care costs, the Republicans would be wise to hold off doing anything about it until they do have the presidency and both houses of congress.