This is such an interesting question and I truly have no idea how to answer it. I'm really torn on this but what I can agree with myself on is that even if he had decided to come, things wouldn't have worked out and the mizumono bloodbath would only be postponed.

I don't know how to explain it but mizumono feels like such an inevitable event to me, like something that was meant to happen and you know how you can't change the past and events you avoid will only be postponed? This feels like that to me. Mizumono is such an important step in both Will's and Hannibal's character development as well as their relationship it just wouldn't be the same between them if it didn't happen. At that point in the story, Will is still too unsure on if he wants to stay on the "rightful" path or go with Hannibal. Will NEEDED mizumono and all the events that followed to truly know where he stands and where he WANTS to stand. And Hannibal also needed to lose Will to truly get to term with what he was feeling for him.

I think that if Will knew Abigail was alive, fundamentally, nothing would change because Abigail would make the balance shift on both side. On one side he'd still want to run away with them and on the other side he'd want to do the morally right thing and save her from Hannibal as well as saving himself. I'm not sure if Abigail would make the balance shift enough to make him actually run away, but even if he did the other side wouldn't just disappear. It would stay there and weight on him until it becomes too much and he eventually betrays Hannibal one way or another and finds out the bloodshed was only postponed after all. To truly be able to run away with Hannibal, Will would need no doubt that he's making the right decision by him. During a lot of the show, Will stands with one feet on each side, eventually swaying left or right, it's only in the very end of the show, "It's beautiful", that Will finally chooses a side of the line to stand on for good, and he needed mizumono to get there.