Just to be clear, I don't think Trump himself is going anywhere if he loses. He will continue campaigning, first to try to overturn this election and then to basically start looking ahead to 2028. As long as he's alive, he will do everything in his power to remain the MAGA king. And his base will not desert him for anyone else you named in your post, never, under any circumstances. If he loses this election, he immediately becomes the favorite for the Republican 2028 nomination, which he will win if he's alive and isn't, like, actively falling asleep and drooling at his rallies.
I also think you're looking at this thing too narrowly by focusing on career politicians as the leaders of the Republican Party. They're not anymore. IMO people like Carlson and Musk are much more likely to steer the post-Trump MAGA coalition (and by extension the post-Trump Republican Party) than the people you named. Celebrities and/or people with large "independent" media voices; these are the future leaders of the Republican Party, at least in the immediate future. Unless and until there is a major shakeup in the American political landscape, whether caused by domestic or international calamity.