Rowdy... sorry to hear about your dog's declining health. I know very well how hard that can be as my family just had to put down our beloved golden retriever of 13 years last week.
It was a similar situation where he couldn't really move much at all anymore, and had stopped eating. It was a difficult situation because he didn't look like he was in pain, but you could just tell that he was at the end.
We took him to the vet and after a series of (expensive) tests, we found out he had a large tumor on his spleen. We could have opted for surgery, but at his advanced age he probably wouldn't have made it through it and even then it wouldn't have likely solved his problems completely.
In the end, the decision became much easier because he couldn't even get to his feet anymore... not even to go to the bathroom. It was very tough, but we knew we were making the right decision. And when the time comes, hopefully it will be a clear decision for you as well.
I never thought I would get so emotional over a dog, but it was a very rough few days for me.
Anyway, I hope all goes well and that your friend is at peace when the time comes.