You should be able to die while doing Zazen I've heard Muho mention.
I have seen Jundo sit through an Earthquake.
Letting go of yourself.
Shall we "use" Zazen for our own profit? We can't really. No matter how hard we want it, we can never ever have it or use it. There is just this. This emptiness. Who are you really?
We can talk about habits, tendancies, idealism, misunderstandings, compassion, truth, but none of that is about what is happening on that cushion when you drop any notion of who you think you are.
We are going to die sooner or later. Of course we are not sure of that and we drop that notion in Zazen. However, if one hasn't done that yet, they should realize that death is eminent.
Don't avoid the obvious.
Gassho and good luck