The GOP would probably keep its rickety collection of primaries, caucuses, and conventions that no one actually gets to participate in. (Three states, including a mid sized state like Colorado, flat out held unelected state conventions to select delegates on the GOP side in 2016)
Honestly I would not be surprised to see the GOP increasingly move away from popularly elected primaries (especially if their party remains united around Trump's successor) consider not only those three states from 2016 but also all the states this year that have cancelled their primaries all together
