Worse, should he win and decide that two terms isn’t enough, who is left in the Republican Party to stand up against him?

Almost everyone.

Unlike the 2020 election, most Republican officials don't gain anything if Trump were to be successful in converting the U.S. into a Trump-let dictatorship. Nearly all Republican House members and Senators would have been better off it Trump had won the 2020 election instead of Biden, at least on the surface. They have their offices either way, but they have more power and more influence if the President is a member of their party, rather than the opposition. So they were very tolerant of all of Trump's legal efforts to contest the election, and several were supportive of even the crazy electors gambit.

But letting Trump throw out the entire Constitutional framework of our government and not have an election at all? That's a whole other kettle of fish. Now their power and influence - all of their power and influence - is going to be destroyed. John Cornyn (for example) has a lot of power as an influential Senator, and while he would prefer a Republican President to a Democratic one, he has all that power and influence regardless. It comes from being a powerful Senator. But in a dictatorship, he loses all his power. There's no rules any more, there's no more elections, no more laws - if President-for-life Trump decides he wants someone different to be the senior Senator from Texas, that will happen, and even if it doesn't nobody ever has to listen to him any more.

Unlike 2020, this wouldn't be Trump trying to take power from Biden and the Democrats. This would be Trump taking power from everyone. They have every incentive not to go along with it.