@eoe,
I didn't believe it before, but I believe now because I've seen it:
Some people do really die of a broken heart.
Someone dear to me was fiery, sharp, and still in relatively good health right to her late 80's.
But it was when her brother, my stepdad, passed away that she started to lose her twinkle in her eye and she got sick that year. Passed away very suddenly not long after.
It was my stepdad that had said "So and so died of a broken heart" and I would laugh. But he was right. It is possible.
I want to live as long as I can so long as my heart, mind, and body will cooperate with me. If I'm ever so heartbroken that my will to live goes, I've decided I'm not going to fight it.
Some people do decide when it is time for them to go. And I do believe we have that power to make it happen, or to extend ourselves longer if we want.