I don't necessarily accept the premise of him fading away but I doubt by then he'll actually still want to go through the same process only to very possibly lose again. The possibility of him dying or being in jail by 2024 is WAY overblown by wishful leftist hacks and isn't likely, so even if the nominee isn't him he'll likely be a critical part of the Republican's outreach and voter turnout operations.
Remember when claiming that he'd try to stay in power illegally was considered something made-up by "leftists hacks".