One small sad note over the holidays (updated)
Respiratory ailments would be the worst for me; I would hate to have emphysema for years, etc. Thankfully, he seemed to go fairly quickly (in a few hours) and did not suffer long.
He WAS a fairly well aged Cavy, being about 2-3 years old when my wife and I rescued him from the local shelter. He had a deformed foot that never seemed to bother him at all. He got around famously despite this.
We miss him already.
It appears as though his respiratory problems were due to congestive heart failure.