Alright, so after a bit of research in the small spare time I have, I have a few leads on who might own the rights to The Lost Dungeon of Souls. Considering Sierra was the publisher, and Activision now owns them, the rights are either at Activision, or at one of the Troika games co-founders. The latter seems more plausible since after a few reading I have found out those guys get emotionally attached to their projects and considered Fallout to be their own. So right now my next step is to contact one of, or more, Tim Cain, Leonard Boyarsky, and Jason Anderson.