I just do not see this fight happening if Wilder is paid money to step aside to allow a Fury-Joshua fight to go ahead. It makes more sense for him to make phenomenal amounts of money for doing nothing.
Would Wilder prefer to fight Fury and risk losing again and never end up fighting Joshua or would he prefer to let Fury and Joshua battle it out and then fight the unified heavyweight champion instead? HE can get paid two huge sums of money, one for waiving his right to invoke the re-match and the second huge payment for a winner-takes-all-the-belts fight against the winner of the Fury-Joshua fight.
This scenario could happen if Wilder have the wisest advisers on his side. If the third fight happen, chances are high that he gonna lose and might end his career for good. It is just pride that holding him now for not taking that step aside money. He could have tune up fights to bring back the confidence in him and build the hype for their trilogy in the future. For now, boxing fans want to see how Joshua will fare against Fury and that fight brings a lot of money to boxing.