I went for that in my last playthough and was happier with it than I was with the Blade of Avernus option. I saved the Duke, found Ansur, Wyll said he wanted to be Duke and told me what he would do - all of which sounded better than killing devils and demons that Zariel doesn't like.

Back to camp I encouraged him to become Duke and in the epilogue
he went even further than I expected "declaring that he had formed a parliment in Baldur's Gate"