In 2003, the game was canceled and the Black Isle employees were laid off. At that time the engine was about 95% done. You could create characters, use skills, perform both ranged and melee combat, save/load games, and travel across maps. A tutorial level was done that would let the designers do all of the above. All areas but one had been designed. About 75% of the dialouges were done and at least 50% of the maps. BIS already had many of the character models and monster models.
So it sounds like maybe you could get about a longish demo's-worth of actual gameplay out of it - at least enough to mess around a bit. Sort of up in the air at what point you'd run out of stuff, and it'd be a shot in the dark if any of the quests worked, etc.
Sounds like it'd be quite an effort if it was just released to the community to finish - and who knows how much backtracking you'd have to do (I can assume they hadn't been working on the game with the idea that someone else might come along later to finish it - so who knows how well documented their programming is, etc.) Still - there's likely enough interested parties in the community that it'd at least be an interesting project to work on - even if it was something that the fans never quite got completed, it's not like we'd be losing anything in the process. So maybe it would be worth just releasing the work-in-progress and letting the fans run with it.
There might be some legal issues to deal with on that front, though.
It'd be nice if Bethesda would go ahead and put it out, though. That might more likely involve hiring out another studio to work on it - so it likely depends on whether or not there's enough market value in spending the resources on that.
Heck, I'd love to play it, I remember drooling over the tech demo vids when they were first shown - it looked like that game was going to be right up my alley. But if "playing" just meant running through what I could of the game until it crashed (95% percent complete engine means there's likely to be tons of game-breaking bugs. And even if 75% of the models and characters were finished, there's no reason to believe that some of the remaining 25% weren't the ones you were supposed to run into first - there might not even be much of a game to play at all,) I don't know if I could bring myself to go through that torture - like if all you could ever do is play the first half hour of Fallout 1 - for myself it'd be better just to never have touched it to begin with.