you could just convert the game system and expand it. I'm sure you can buy replacement dice from fantasy flight games so you ought to be able to get a second set of dice here.

Decent is based on the concept of the dungeon crawl. so you shouldn't need to modify the system for an RPG too much. I'm willing to bet you could extrapolate out the combat system for social situations and skill. Heck they used to even have a custom character creator on their website. I'd head over to Fantasy Flight games and see what I could find.