So I've been thinking that I come from a strange camp. We seem to hold to the belief that there comes a point where life is not worth living. That if we can't do the things that bring us joy in life then it it time to go. The older I get the more people I run into that seem to view it differently, that seem to think that life in and of it self is worth preserving. I know my family is probably a little extreme on their views, but I wonder where the average lies on this. At what point is it time to let someone go and at what point is it time for you to go?
That said, I do believe that if you really truly aren't happy and aren't able to become happy, ie old age, being entirely disabled, etc, then perhaps it is time to let them/yourself go.