Yes, it's not necessary but I doubt there will be an interest in GGG to have a trilogy if Canelo will lose on Bivol.
And from what I understand, promoters or organizers both require GGG and Canelo to win their respective fights as part of the mandatory pre-requisites before making the trilogy happen. Maybe it's best for them to officially organize the trilogy if both boxers came from a win.
I'm not just sure about how true it was.
There will be always an interest in GGG to have a trilogy with Canelo even if the latter will lose its fight against Dmitry Bivol, why? It is because GGG is not Bivol, he is always asking for the 3rd fight in the past even if Canelo is not interested, he wanted to close the fight because their standing is 1-1. But I think their trilogy will be postponed if Canelo will lose against Bivol as he will likely go for a rematch first.
I'm also not sure of their agreement but as far as I understand it, Canelo already signed it because it was a two-way deal including GGG but the money talks isn't yet agreed so the deal is not yet done. Also GGG have not signed the deal, don't know why because the last time I heard he was still busy preparing against Murata. Either way, we will know about it soon.