I don't think the possibility of Usyk being stripped of the IBF belt would be any threat to the rematch with Fury. The rematch will happen regardless of the IBF's decision.
That's simply because the only way for Fury to save his face/legacy is to go out there and take his revenge on Usyk. What other option does he have? Refuse to fight because the number of belts is not quite the same as in their 1st fight? That would be nonsense.
As for the IBF belt, it's a bit weird that we're only a few days away from Hrgovic Vs Dubois and nobody seems to know whether it's going to be a fight for the belt, interim belt, or no belt at all.
I think we can rule out the belt, as Usyk is on medical suspension until 2nd June, unless the IBF really want to strip him (I don't believe they are) and will find some loophole to do it before the 1st.