There seems to be a growing conventional cool kids wisdom that if the Republicans manage to gut ACA one way or another then Dems will just say fuck it and pass some version of single payer (recognizing that to some degree "single payer" has become code for a variety of things which might not actually be single payer but close enough, including massive but not universal expansions of medicaid/medicare) the instant they have majorities in the House and Senate. I think this is optimistic.
I would certainly be happy to be proved fucking wrong.