Speak with Zureetha Fargaze.
I think it would be good for you to gain experience by assisting her. Be sure to tell her that you assisted with the imp problem, she'll probably have a reward for you.
You have done well, <name>.
Oddly, one of the rewards (Primitive Walking Stick) is not wieldable by beginning warlocks - they haven't learned the staff skill yet. (The icon is red.)