I'm only mid thirties and I'm totally over it so I'd think they would be pretty much at peace once they are pushing 80 or whatever. I wish I would contract something short term and fatal though. Lots of sympathy, morphine, family around me etc. Being dead doesn't scare me, but everything up to that point does. However much less so if I pass away from natural causes.
A natural end can be anything on the spectrum from a heart attack to years of suffering. Every day i see people struggling to go about their lives despite all sorts of physical problems or handicaps and admire them more and more and despise myself for having quit. I did some voluntary work with elderly people for a while and for anyone trying to life themselves out of depression i'd recommend it.
Being occupied, having a social network and routines, these are reasons some people might cope better than others. My father used to look forward to his chemo sessions. It forced him out of the house, there were nice nurses around and other people he could relate to and not be an outcast because of his illness. When he was unoccupied and alone, it was hell for him much of the time, the thing we don't see.
He spent 30 years drinking and smoking excessively and being fed up with life, probably having suicidal thoughts. When he was diagnosed and given 18 months he just wanted to live and there were times afterwards when i had never seen him happier, also times when he was deep in the pit.
At the end he understood everything about life and death and was at peace with it, something at least