Wow, a mysterious, powerful guy, that'll show up later and completely derail the story and then gets transformed into a useless side character used for comic relief
I agree with the guy, if you've got a golden goose then why kill it?
Now the people who were depending on the industry will be out of a job, no more adventurers will come to the city for the profits of the dungeon which in turn will kill all businesses.
They should give the sparkling potion...