If I'm not mistaken, Microsoft now owns all of the old Sierra IP (if I'm not mistaken, the chain of custody was: Sierra -> CUC -> Cendant -> Havas -> Vivendi Universal -> Activision Blizzard -> Microsoft) and I wouldn't expect Microsoft to sue over old source code to a 40-year old game engine with a graphics resolution of 160x200. In fact, given that they've been gradually opening source code for DOS from the same era, they might even be convinced to make an official release of it.