What is so sad about a person terminally ill having some say about how and when they will check out?
Suicide is not legally sanctioned in the USA.
If the person themself denies medical care (including a feeding tube) then that is moral.
If others have less-than-pure motives for denying care for a ward (and that's what we're talking about here) then that's immoral.
What methods of "checking out" are you talking about?
To have an inalienable right to life and so forth means not only that it cannot be taken away. It means that you cannot willfully set it aside. You have no right to sell yourself into slavery and nor can you contract for your own death. To claim a personal right to end your personhood is intellectually absurd and by definition irrational.
Or it used to be.
Nothing, in the hands of honest people who do not have an obsession which drives them toward the result of death over life. Necrophiliacs? It would not be appropriate here to go into the fantasies of people who have this problem.