So if someone has a written directive that states, "Please shoot me in the head if I become incapacitated and can no longer take care of myself" then it becomes our obligation to fulfill their wishes? People do not say "Please, starve and dehydrate me to death for 13 days if I become mentally incapacitated." And even if they do so, is that the right thing to do? Kill someone just because they asked you to? I'm sorry, I just don't think that's right.
No, It would be more along the lines of, "Disconnect my body from whatever is keeping it artificially alive."
If you don't agree, then be sure to let people know. I'll honor your wish to be kept alive.
Will you honor mine to die?