Do you mean Spence will stake his belts for the rematch with Thurman if he loses here? What will be forced is, Spence will risks his belt at 147 and might possibly face Crawford although as I said previously, there might not a chance now to see Spence fighting at 147 due to some problems.
I mean that's not possible since if the rematch will happened with Thurman, it will still be in 154 and his titles are all in 147.
I don't know though the rules of what will happen if let's say, Spence will ask for a rematch with Thurman and if he's still eligible to do that without vacating all his titles at 147. I think that's a rare case to happen or I just missed some same scenario in boxing history.
What I think is that we might see a different scenario once Thurman is able to defeat Spence at 154, there's a strong chance that the latter will ask for a rematch but since a rematch clause wasn't written on their contract (I suppose), Thurman has the choice to decline the offer if there's no belts at risks. And if a rematch won't materialize, Spence has two choices, first is he will vacate his belts at 147 and second is that he will defend his belt at 147 with a risk of facing the boxers he ducked. And this time, I think that their influence won't be used even if they wanted to because the WBC is already under criticism because of this fight.