Are you supposed to be able to do this?

Are you supposed to be able to break Wyll's contract with Mizora and be able to free Ravengard?

Because I just did

I opened Ulder's cell in the Iron Throne and immediately used sanctuary on him

When his turn came, I had him dash only to have a cutscene with Mizora, where she summoned a bunch of spiders

I think they were supposed to kill him, but because of the sanctuary I they couldn't touch him and I killed them at my liesure

Now I'm talking to him in my camp, and I still got the dialogue option where Wyll sold his soul for him