So we all know the play if Trump wins the election, and if the right gets the Majority in the House and Senate.
What happens, if Biden wins and we lose the House and Senate?
Immediate Impeachment? Obstructionism to the levels we have never seen before? Could the Courts become a ghost town?
What happens if Biden wins and we gain the House back?
Will MAGA just claim voter fraud, and riot again? Will Texas continue to ignore orders from the SCOTUS? What level of discourse will we see from the Right?
Trump is going to lose and take others down-ballot with him. Republicans do well when turnout is dampened, and that only happens when people are unbothered by both sides, for the most part. Biden bothers the right, but Trump bothers the left, right and center. He's angling for control of the RNC, and he doesn't have a good track record of endorsements or spending in statewide races. He's going to spend more on himself, endorse those friendly to him, and probably cost republicans both chambers (again).
I think your last scenario is the most likely. Let them pout and moan. Law enforcement will be ready, and we've already heard this song before. It's Trump's greatest hit. It won't sound the same next year, after hearing about it for the last five (Trump started his election lies in early 2020, or even longer if you count the Iowa caucus and 2016 popular vote lies).
Instead of republicans worrying about whether or not Biden is going to be replaced last minute - that's not going to happen short of death or incapacitation - they ought to worry about their own candidate, slipping off the cliff into insanity and tons of court cases ahead of him.
Anything is possible, its just hard for me to envision a guy who lost the popular vote twice somehow doing better a third time. Is Biden truly any more hated by the right than anyone else on the left? I don't see it. He's just old and without Obama's appeal. That's not harmful enough to hurt his chances, imo.
Remember, we heard a lot of similar things about Obama - "Blacks don't like him as much as it appears. He hasn't really done much for black people." And every once in a while, they'd trot a black person out on Fox News to echo those statements. He still won reelection. And Biden will too.
I think republican infighting is too big of a problem to make them a serious threat to America as a whole, though they'll certainly try. That infighting isn't going to decrease with Trump's hand-picked family members at the head of the table.