Spoke with Awesome Doc for awhile this afternoon. All Joey's bloodwork is complete and it isn't good. Not only does he have CRF, but also Hyperthyroidism. Really no treatment for a fellow of his advanced age, as a major side effect of the meds is loss of appetite, which he simply cannot afford. And any surgical intervention (aside from being entirely too expensive ... yes, I love my little man, but it is simply out of the question) has the very potential side effect of death due to anesthesia problems (e.g., he'd never wake up).
The Hyperthyroidism also rules out the Lactated Ringer's subq, as it won't do him any good. Awesome Doc says that's actually not so bad, as it would have put a lot of stress on his heart, which she's not entirely sure he could have handled all that well anyway (this being the kitty with a heart rate so fast she was unable to count it).
Bottom line is that as long as he remains comfortable and continues to eat, drink, and evacuate with no problems, Joey's good. Right now he's at 12.5 lbs. Awesome Doc assures me this is not terrifically underweight, especially for a 17+ year old, but he can't support healthy body functions below 11 lbs either. It's such a small amount that I'm all "What?!? Seriously? That's a glass of milk!" Completely forgetting the whole percentage deal ... you know, where 1.5 lbs is actually 12% of his body weight, which is significant, especially since it wasn't that long ago he was once a muscular 20 lbs.
So anyway ... best case scenario is Joey falls asleep one day while he's still in this condition (no pain, stable medically) and simply slips away to visit Ben. Worst case scenario is Joey develops some other problem or drops below the 11 lb line-in-the-sand, in which case I'll bring him in and Awesome Doc will euthanize him.
I'm surprisingly okay with all of this. Knowing what's happening has taken a load off my mind. My top priority is to ensure Joey's last days are lovely, and to let him go comfortably and with dignity, no matter what. I owe him.