Ok, so I gave him some food earlier that the vet sent home with us. It's Royal Canin Recovery RS and at first he was hesitant. So I put some on his mouth, he licked it off, and then cautiously started taking small bites. After a couple of small bites, he went for it like he was starving -and I'm sure he is. After an hour he still hasn't thrown up, so this tells me a couple of things.
His liver is likely fine, probably not fatty liver syndrome which will use fat from the liver to compensate for lack of nutrition, making them feel full, so they won't eat, but causing permanent damage. And, with no throwing up his stomach and intestines are likely good.
So, I never gave him any of the pain meds the vets sent home with us, and he ended up eating 4 or 5 more times last night. Today he has eat twice, he has cleaned his fur, and he spent some time re-exploring the apartment since he hasn't been up and around for a while.
I think the entire issue was that he just needed something to keep it from hurting while he ate again, to get past the food=pain association - it's the only thing I can think of. 2 vets couldn't figure this out, even though we mentioned to them we thought something was wrong with his mouth due to his gnawing behavior. I know where I will be going again when I need a vet, that's for sure.
If it's pain from a tongue injury, that's great! Not that he got injured, of course, but because he should be fine once he has healed. Chronic conditions are much more frustrating . that he feels better soon!