I wrote a response before I headed out, but it looks like I forgot to hit "post." Thank you all for the -ma. I took him in last week and they kept him over the weekend for kidney stuff (IV fluids). I took him home on Monday with instructions to come back in if he stopped eating for 24 hours, which was last night and this morning. So, the vet ran another panel, and he'd lost ground again. There wasn't anything to be done that would have a long-term benefit, and, as I put it and the vet confirmed, his quality of life was and would be crap, so it was time to let him go. I was there with him, which seemed like the right choice in this case.
Again, thanks for the -ma. It went, I suppose, as well as could be reasonably hoped for under the circumstances