If the court rules that ACA can't give subsidies in those states, that probably throws a few million people off their health insurance. Congress could restore the subsidies, but I don't think that will happen with the GOP in control. They won't care about the suffering of a few million people, who are perhaps mostly Dem voters anyway.
However, the GOP may want to avoid looking hard-hearted, so they'll probably figure out how to blame this on the ACA law, and its complexity, and how it was rammed through without being well-constructed, so it's all the fault of those Dems. They may be able to get away with that story because enough of it sounds true enough.
The GOP may even get extra lucky, and the loss of the subsidies will send Obamacare into a death spiral of massively higher premiums and fewer people covered. Again, they may be able to cause this death spiral without receiving the blame. It's hard for me not to believe that many Republicans are hoping for exactly this outcome.
But at the end of that death spiral will be some very big problems, and ultimately the GOP won't be able to ignore them. There will be a massive number of uninsured people, which will include plenty in the middle class or former middle class, and they won't be forgiving the GOP for the end of readily available health insurance. The GOP will have to come up with an answer, or a partial answer--enough to keep them in office. Maybe they'll cobble something together, but that would be several years down the road. In the meantime, the road will be littered with people bankrupted by healthcare costs or dead from lack of coverage. I doubt the GOP will pay a high enough price for what they wrought--if it plays out this way. I hope we don't get to see if it plays out this way. It's too big a risk for too many innocent people.
Extras. Bernstein is much more optimistic than me. This WaPo column is more realistic in the dangers.