I was wondering that too. I don't know the answer to that, but I would assume it could be done. If all the Republican candidates are saying they can do away with something so complex as Obamacare, I would think they could reverse this. Deserves some web surfing.
Where'd you hear that? All the Republican candidates want to do away with Obamacare? (They may be saying that just to get elected.) Do "all" the Republican senators and congresspersons want to get rid of it? It takes 100% agreement to undo the massive injury that illegitimate law has caused the United States. Look at Roe v. Wade as an example.