I couldn't find the developer's contact info, so I'm writing here.

I was in the S corp building, went with the mouse into the vent. Everything was normal: I had only mouse selectable, Dropsy and the dog were disabled. Then I saved the game to see, what would happen if I get shot. Still, everything ok, I got teleported outside. Then I loaded the game.

What happened was that the loaded game had me as a mouse inside the laboratory, but I also had both Dropsy and the dog available, but beyond the screen limits. So the game didn't store, that I was in the mouse-only state, it seems. If I exited with the mouse into the foyer, the game would put me in the "mouse-only" state. If I went back inside through the vent, I'd be in the Dropsy and the team state. As a result, I softlocked the game.

Lesson: don't save, when you don't have all your team members available.

P.S. I've read, that GoG has an older version of the game, than Steam, so it might have been fixed there.