Are we sure we are all talking about the same guy? I mean Deontay Wilder literally went 42 matches without a loss, he had only one draw which was a lot of controversy but even if we consider that a loss, he would be 42 wins and 2 losses right now, he only has one loss which just happened in all of his career. Dude is also just 34 years old in a sport where even 40 years old people are fighting today, maybe not in his weight class but it certainly happens, with the advancement of technology and medicine sports players are playing well into their 40's now and he could very well do that as well.
I am not saying he will be a great boxer from now out, he had his best years behind him, but he could very well challenge for a new fight one day, which he might win or lose I don't know.
Who is he going to challenge?
Tyson Fury is likely going to fight AJ and grab all of the belts once he wins.
We can only assume that Deontay Wilder will execute his rematch with Fury and they'll fight next. Based on their previous performances, Fury will smash Wilder once again.
Then Fury will go and grab all the belts and become undisputed.
Do you really think that Wilder will get a title shot before he retires, given the fact that he would probably also get beaten by Oleksander Usyk and get knocked down the rankings?
Realistically I don't see him getting another title shot after he loses to Fury again in a few months.