Sorry to hear that, but no one, or anything gets out alive. Sounds like you made his last years, very worthwhile. I think that is a great idea to spread his ashes, in the river. I know the feeling, and it is the same with the dogs, I had, and finally lost, and the cats, and any other pet I have had. I have always, said, if you aren't going to treat a pet, as part of the family, then you really don't need one. Again, sorry for your loss.
Wayne