The game is simultaneously in my account already and not yet available for purchase. Which is amazingly fitting, if you've played it.

I wonder if there was an offline installer if this game could still be played.

Did it playable by GOG Galaxy? GOG Galaxy version is still available?
Offlain version is available, in Library, in website version of account Library. And it is perfectly playable (make sure FPS are limited, use integrated video if game screen flicker (Nvidia drivers only, and only on Win) or some basic d3d wrapper, or GOG DX wrapper from Blood Omen - since it is Nvidia issue it happen on Win7 too).
It already have compatibility fixes, including community ones. But some legal issues.