It seems clear that the plan is to game the system as much as possible before then so Republicans never have to win an election again. If they can do that, they don't need Trump - the Trump administration will live on.
Please note I am not planting a flag here, just making an observation.
Republicans aren’t some consistent viewpoint. It’s a big tent that’s (somehow) united by Trump. Even if Republicans came to completely dominate politics, they may have their own schism and we end up back in two party land.
Thought that may still be a more chaotic two party land than we have today. Who knows what the future brings.
(There are many models, and all models are wrong, yadda yadda)