Night song💀,isobel /last Inn ...what will happen if...

Third run and 1st as Dark Urge i'm starting as a "good" but not THAT good...i want to leave Shadowheart do what Shar ask to her...what will happen next and in act 3?

I've heard that is the same if Isobel get caputured for the Last inn...is that true?

And about act3? What will happen to Shadowheart?