It's always sad when we loose one.
He was acting strange, and I took him to the vet he had some behavioral problems that were not able to be helped.
That is one thing that most do not realize ... often, with chinchillas, as with humans, if there is something bad wrong ... towards the end, their personality will change and they become hateful, mean or their personalities will reverse to what they normally are. Sometimes the change is slight, but often it will be drastic.
Did you get an autopsy to find out what killed him?
Did he have any cagemates?
Jo Ann