If you finished the Poison Quest and the Plague Quest then he will be gone and you cannot finish that part of it where he tells you the key was stolen and he knows nothing about the poision. (As far as I know you really dont need him to tell you this you dont get anything from it). But you should of still got the exp when you talked to Hugh and all.
If you talk to Hugh after finding the key you got the points and all. When you go to the Town Watch and tell Commander Ralph you will get an invite into Castle Stomfist.
and if not mistaken that finishes the quest all the way.
Good luck to you.
J.W.
