Zachski: Very useful!
However, I had a thought - after you save the Dry Domovoi (Which you can do without talking to the Inn Domovoi), what happens if you enter the main hall at midnight, enter your room, and then re-enter the main hall and try to open the cabinet?
Also, I can confirm that the "Innkeeper thinks his daughter is still gone" thing is probably an inherent part of the game - that is, it'll eventually cycle *past* the "Yay the daughter's back!" events and go back to the standard events, which also includes him being cold to you and might believe his daughter's gone.
From my experience, it isn't the second visit beyond midnight that triggers the doll to be retrievable in the main hall. It is the second attempt at dialog with the Domovoi. I demonstrate this in my speedruns; I talk to the Domovoi, hit escape to cancel the dialog, and immediately talk to him again. Even though the doll dialog never appears, I then take the doll...
... and immediately, after writing this, I remember my old route in speedruns, and I believe it was the second visit. This may be an odd example of either/or in QFG. :/ I've changed routes so frequently as I've learned faster tricks I've forgotten old ones. That might be worth a look.