Afaik, Mizora is now waiting for something bad to happen with Duke Revengard, because somehow Wyll's refusal to sacrifice his soul for the second time sealed another deal that Duke has to die. Somewhen.
She does break the contract entirely (depending on your choices regarding his father's fate), there's no more 6 month wait. The 6 month deal you make in act 2 is more or less just a red herring since it'll never come to pass unless you personally kill his father - Mizora will always return with a "all or nothing" deal in act 3. Unless she doesn't offer to break the deal completely if you never did the 6 month deal? That I don't know.
Either way, she just lets him keep his powers until the Absolute is dealt with because she wants revenge for them capturing her. That's why she's sticking around.
On the general topic of Wyll's romance, I just had a thought due to another discussion... Why can people who didn't start Wyll's romance in Act 1 get the dance in Act 2 at all? Mustn't it actually be a bug? Every other source I'm seeing says that, for other companions, you have to start their romance in Act 1 to be able to get romance content in Act 2.
It just means his romance doesn't actually start in act 1. And yes, every other companion needs to start in act 1. Lae'zel/Astarion want to bang you, Gale wants the weave scene, Shadowheart wants her date, Karlach wants confirmation you want her. Wyll.. nothing. Though if you're rude to him perhaps you'll never get the dance scene, even with high approval? Unlikely though.
It even seems to be queued behind other romances. I have a save where I'm on the path for both Karlach and Shadowheart, and I can only get the dance scene after I triggered the Karlach cutscene (which won't happen until you fix her up at Dammon) and then break it off with either of them.
