It's in digital ownership limbo like a lot of stuff.
Activision claims Zenimax owns it because they bought id and the IP, which is technically accurate, but Activision and Raven would have all the actual game stuff stored somewhere and apparently nobody asked for it? Activision has said they wouldn't do anything about Zenimax selling it, but I assume Zenimax would have to get the assets and everything from Activision to put it out, which probably means a side deal of $$$. I'm assuming that if id had it all there wouldn't be much of a problem. (Like RTCW and Quake 4 which made the trip over from Activision just fine.)
IIRC, on PC you might as well just pirate the whole thing because you should crack it anyway because of the DRM it has. (And I want to say cracking it lets you use something to change the tiny FOV and stuff too.)