I've had this conversation with my mother before. As far as we can see it, there are only two reasons to stay alive.
1. Duty
2. Curiosity
Once those are overcome, there is no reason to keep slogging.
I'm not now suicidal, but I have been in the past. I still sometimes get a flash through my head of ramming my car into an overpass or some such when I'm driving. It's weird how strong the impulse can be. And I currently have no reason whatsoever to want to do such a thing.