Rogash spent a considerable amount of time in taverns and before finding his new friends and a taste for revenge against the 'man in the white plumed hat' and by extension Duran--he was in the process of drinking himself into an early grave.
If my memory serves we had reason to believe that Duran and company were having trouble in the sewers with some part of their own operation. Correct me if I'm wrong IG. That and curiosity about the mysterious noises were his motivations for getting involved. Interest in Vardi and the Alchemist came later for him. However, I believe we did establish that he knew Vardi and would be interested in helping her and Loddie out.
After encountering some nasty traps, outsiders and chaos beasts down there he feels some need to find out what is going on.
Anyway, I'll make some revelations in the IC thread now.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.