In a way it would be sad to see but probably the optimal path for both of them is to retire at this point.
Usyk has done all he could have, he's now comfortably an all timer heavy and even an all time pound for pounder and no other person fighting right now could reasonably enhance his standing in the game of at all plus while he still performs at high level age catches to all, one could see the allure of retiring with such a pristine resume unblemished.
As for fury he did show he really was up to it and perhaps in another world where he wasn't short of motivation his and usyk's place would be reversed and while he did show up I do think he's on his way down durability wise and will be worth it for him to finally get knocker down?
The best future fight for both would be a rematch, fury could take one with Joshua as to finally settle that one, both have now made plenty but ultimately there's away more to make.