I suggest they do the opposite. Since he is a lame duck now, make him stay in office and the GOP suffer the consequences for the next two years. So that, by 2028, the whole USA will go blue. Don't give the GOP a handy escape hatch today by ejecting Donny and putting JD Maybelline in the Big Chair in his stead. Vance is far more dangerous than Trump, especially at this juncture, and far more capable of creating obstructions and havoc.
However, if you DO want to bargain, tell Trump a deal is on if, and only if, he sacks every one of his Project 2025 infected administrative team and never re-employs them in any capacity ever again. Miller in particular, but he is just the first turd in the heap. Further, that Trump agrees to rescind every pardon he has issued, in particular the J6 pardons, and instructs that those pardoned have their previous sentences resumed where they left off. Knowing Trump, if he gets to keep hold of the pretend big bus steering wheel, he will do that. Loyalty is not a word he knows.