Two things:
First, for there to be a RE-union, we would have to be doing it AGAIN!
We could still have a gathering of some kind without hurting my feelings, any.
Second, diabetes sucks, but if you take time to take care of yourself, it is something that can be easily controlled for a very long time. If it is Type 1, then it is more difficult and has more impacts, but it can still be kept from having serious side effects for most of a person's life... as long as they keep their weight (and a few other issues) controlled.
To be clear, did the ex say that your son was going to die in two years, or was he informing your son that he (the ex) was going to be dead in two years?
In either case, I'd definitely want to find out what brings him to that conclusion, because doctors told me I wouldn't be diabetic for another 10 years or so, and they were about 70% off in that guesstimation. In the wrong direction, unfortunately.