Hey so, I figured out how to fix this since I last found your post.
Go to Gortash’s coronation.
Exit and meet Mizora on the bridge.
Immediately to camp and turn down Mizora.
Exhaust all dialogue with her and Wyll.
Leave camp back to the bridge where you talked to Mizora.
Exit to Baldur’s Gate ON FOOT through the path. DO NOT FAST TRAVEL.
Then you can check to see if this worked by doubling back through the exit you just came from. Going back in to the coronation room and seeing that is has… changed…
…you’ll know it’s changed. Trust me. The Duke will be gone to say the least.
Hope that works for you! I posted this on Reddit and I’ve gotten a lot of success stories.
