We don't "all" know that... I've always had a sneaky feeling that Fury-Usyk only happens once. Part of this is because I have Usyk as strong favourite, but I think it'll either be a clear Usyk win and Fury (having lost his 0) won't bother trying to avenge it -OR- Fury will cheat/spoil/fluke a win and then retire (or get caught with PEDs, possibly deliberately ) to avoid losing a rematch. Could be wrong, but this makes more sense than the rematch happening IMHO. Then again, that's if they even fight at all.
I agree have them fight. And we will see who is more sore. Fury after getting spanked by Ngannou or Usyk after getting spanked by Dubois.