Okay, apologies - you can *actually* tell Mizora to go F herself, break the pact *and* save Duke Ravengard.
I hadn't even planned on it, I always assumed you couldn't. It just.. happened that way.
So I went to the underwater complex,
[spoilers]
Mizora intervened as expected, spawned her hell spiders or whatever - they all immediately ran for the Duke to explode - except, the duke was behind my Tempest Cleric with Spirit Guardians and Lightning Charges/Phalar Aluve on. So they just all got nuked and bumped back. One made it through [they can only take damage from it once per round], exploded right on Ravengard's head but Gale automatically had his Arcane Ward projected on him and he didn't take *any* damage.
Walked right out of there with Ravengard in tow, and Wyll's contract broken. Having my cake, and eating it.
[/spoilers]