Dog-Or is much improved from Saturday. He's still clumsy and off-balance and walks with his head tilted, but he was feeling well enough to come for a walk the other day.
We got a little way along the street and he decided he wanted to turn around; I thought we were going home, but he went straight past home and around the corner on the other side. Then he turned around again, and I thought this time we were going home, but when we were almost back he turned AGAIN and went back to the corner. Then we came home. I'm not sure whether he was lost, or meandering, or trying to mess with me, but he seemed to be enjoying himself. He's eating (though not in huge amounts) and he's going outside when he needs to, so yeah, functional. I carry him up the stairs at night and downstairs again in the morning, because he was having enough trouble with stairs even before the vestibular syndrome hit.
So, chalk one up for the vet, and it looks as if Dog-Or should be with us a little while yet.