I honestly cannot see Wilder asking for a re-match - he knows Fury will destroy him again. If Wilder manages to unleash a powerful right hand and catches Fury off-guard he might win but he cannot out box and he cannot outclass Fury therefore another defeat for Wilder is the only result. If Wilder has a few warm-up fights beforehand then tries to get a fight with either Fury then he stands a better chance but inevitably Fury will destroy Wilder again regardless.
Wilder does not believe he will be destroyed again, he was a champion with only one defeat it's just good to give him another chance.. other reason is the money he will get in the 3rd match, and if Conor challenge Pacman to a fight even knowing he has no chance, why not give a chance to a real fighter like Wilder.