We talked to the vet last night. He feels Fasb always got good care. He doesn't feel we did or didn't do anything near the end that would have made a lot of difference.
I'm still bothered by the arthritis issue. Fasb never suffered greatly from arthritis, but there were times we could have done more. He developed arthritis fairly young. At first, the only sign was that he had to "pump" to jump on our bed. He did steps fine and was jumping a lot on things he could take a bit of a running start. The space around the bed was narrow. He had to do it from a standing start. We had never owned an animal before so it took us a bit to realize it was arthritis and put him on a supplement.
We never let arthritis go untreated and it never got really severe, but we weren't always quick to recognize the signs (he eventually went on prescription meds but that was much later).
We also found some quality of life assessments while we were cleaning up the hard drive last night. Read through a number of them and took the "quizzes". Near as we can figure, his quality of life was still very good until near the very end.