A new idea has surfaced in the last 24 hours about what Senate Republicans might do if they can't pass anything else: they might pass a lowest-common denominator plan that only repeals a few pieces of the Affordable Care Act, the parts everyone hates. Vox has a good explainer about how this might work.
"Skinny repeal": If the Senate votes to start the debate, but it can't pass either its repeal-and-replace bill or a straight repeal bill, the last move might be something that just gets rid of the individual and employer mandates. It would be hard for any Republicans to vote against that. (We've also heard a third piece: the bill might also get rid of the ACA's tax on medical devices.)