I think the cancellation of the third fight would be on Wilder's advantage because he need to but some time to bring back the confidence in him as he was battered on their last fight. AFAIK, the rematch clause has expiration so i don't think the camp of Wilder will take a legal action here.
Definitely it will be a big advantage for Wilder so that finally he can reset his mind first and have some confidence before facing Fury again in this trilogy. Yes there is a stipulation that a rematch clause could end, but the thing is that when they outline it prior, there's no pandemic or something, so again, maybe the next time that those boxing lawyers or promoted a rematch clause, maybe they have to think about this kind of scenario.