I think it is unlikely, at all.
We already had a republican sweep in 2016, in a campaign where they promised to kill it. They couldn't get it done, so they killed the nonenrollment penalty, thinking that would destabilize the markets and get insurers to withdraw. That happened to an extent, but more people are enrolled in ACA now than ever before.
I think this belief is naive at best and grossly misinformed at worst.
In 2016 you still had Republicans in Congress that cared about people. McCain, Romney, Cheney etc. Those people are long gone. They "couldn't get it done" was because of one thumb. John McCain's. Had that not happened 50 million people would have been without healthcare. If they control both chambers and it comes up, it will pass, stop fooling yourself into complacency and be prepared to fight by applying pressure to your local reps if talk of it even starts.
We've got plenty of people in our family that would immediately lose insurance. Type 1 diabetics, folks who had cancer before. I've lived in the world with pre-existing conditions making people uninsurable. It is not pretty. And not being able to stay on parent's insurance until 26 would immediately put all six our kids in a budget issue they can't easily adjust to if at all given all the other employement issues in the country and cost of coverage there.
As in many things, history is more complicated than people's memory. John McCain did cast a dramatic, deciding vote in the Senate. But it was not against a repeal of the ACA. It was against the
Health Care Freedom Act of 2017, aka the "skinny repeal," that would remove the individual mandate and employer mandate, but nothing else. Of course, the 115th Congress did eventually change the penalty for non-enrollment to $0, as part of the
2017 tax cut package, effectively enacting the first part, but which in the end did not sink the ACA at all. There were
66 prior attempts to repeal the ACA more thoroughly, but none of them reached the point of drama we all remember.
I don't think naively that there aren't Republicans who would like to see the ACA repealed. But, frankly, it's
more popular than Congress. It's crossover to favorability started, ironically, in 2017. Also, note in the prior link that 50% of US adults have someone in their household with preexisting conditions. And polls show a majority, even of Republicans, think it's "very important" that the pre-existing condition provision remain law.
I'm on the ACA, too. It's not as good as the insurance I had with my employer, but it's an important part of my early retirement. Should I be wrong, I will definitely speak up and fight for it. But I am not panicked, at this moment.