Hrgovic has been mandatory for years already. At this point, the only way they will make an exception is if the Saudis can bribe Hrgovic and his promoter with enough money to agree to step aside. Considering the magnitude of the Fury vs. Usyk rivalry, it might just be more lucrative to keep stepping aside.
I expect Hrgovic to beat Dubois but if he loses or if it ends in a draw, it will play in to favour with Usyk as the IBF could still try to force him to fight their number one contender but Hrgovic carries the potential whereas Dubois does not. In that scenario, the rematch with Fury could go ahead with the peace of mind that
all of the belts will go back on the line and will be made available to the winner. I think that is a fair assessment.
My vote will be the same: Usyk. Whilst I expected him to win on points in the first match he almost got the KO had the ref not stepped in so maybe Usyk will get the KO this time. With that being said, Fury now knows what to expect and what he has to do to try win so I expect he's the one that is going to go hell for leather for a KO as that's the only way he's going to win.
I am not surprised you are confident Usyk will win the rematch, he is after-all an absolutely solid technical fighter but the threat from Fury remains. As you stated, Fury knows what to expect when enters the ring in December but Usyk also knows what to expect too.
It will not be a let down, the rematch should be another stunning spectacle but here is where the difference might be made: Usyk gave 100% and was on top of his game when won but Fury only showed glimpses through rounds 4-6 which was when he clearly dominated and shook Usyk several times.
I really hope there will no nasty surprises before the rematch takes place such as injuries, delays, failed drugs tests or any excuses because boxing fans deserve to see the rematch and also both Fury and Usyk deserve to fulfil the contractual requirements of their rematch.