If Bryan cannot keep going "full time", Mox could destroy Bryan at WrestleDream.
Then that feeds off into two big angles, Darby working his way up to be the one to stop the monster heel champion and win the title at All In. Bryan could return at All In to help counter Moxley's group. Then they could have a big blowoff Lights Out match against Moxley at All Out.
I think that if Darby is going to beat Bryan, they should add on to the Bryan retirement stip to say that he will either retire when he loses the belt, or if he hasn't been beaten he wants his last full time title defense to be at All In 2025. That's his deadline. Because I think that sets it up to where the fans actually want to see Darby win because Darby winning doesn't cost them anything. Unless they are sick of Bryan and wants him gone, a babyface beating him and retiring him is a weird dynamic to pull off.
The idea being "I will either show up on Dynamite after All In to hand the title to Tony Khan and thank him for the opportunity to carry the torch for a year, or I will show up to hand it to the man who proved he was better than me" is a much better dynamic than fans feeling like Darby getting the title ended Bryan's full time career.