Upon completion of Reluctant Steward, Mogrul reveals that Drovas owed him 1000 . He will then demand that the Dragonborn pay Drovas's debt since they were responsible for him leaving Raven Rock. If the Dragonborn doesn't pay him right away he will send his thugs after the Dragonborn until he gets his gold. The debt can be reduced to 500 with a successful intimidation.
The Dragonborn may also talk to Drovas about his debt. First, choose the option "Please be patient, I'll get you your money" while talking to Mogrul. Then, travel to Tel Mithryn and talk to Drovas. He will say he doesn't have the money, but will give the Dragonborn 250 if they are persistent. The rest of the debt will still have to be paid by the Dragonborn.