In a perfect world, Khabib would fight Tony for 30-0. At that point, vacate the belt and fight GSP and/or ride off into the sunset.
If Khabib walks now, I'd like to see Tony fight for the belt (I don't care who it's against). Gaethje, Dustin, and Conor have all had a crack at the undisputed title. Meanwhile, Tony has never actually had a shot at the undisputed belt, and he's done more at LW than any of them. The fact that he lost to Gaethje doesn't affect the analysis for me, considering he shouldn't have been forced to take yet another interim title fight in the first place.