At what point does a person actually cease being a person and just flesh being kept alive?

Based of this question, when does someone stop being a human and become an expensive lab experiment? Many who answered used words like viability, able to survive on its own, sentience, etc to allude that unless the life can survive on its own, apart from the mother, it is not really human yet, so termination of it is not tantamount to murder. If a person suffers an illness that leave them brain dead, if you put a pillow over their face and smothered the life out of them, since they can’t live apart from the machine, would that be murder or quickening the inevitable? What if the person was still conscious of the mind but because of the injuries they could no longer speak, move, swallow, or breath on their own, do they lose ”human points” because of that? If they can’t live on their own, what is the reason for doing so? If a family member sneaked into CCU and put a pillow over his/her face to keep the family from draining their livelihood just keeping flesh warm that never be able to function on its own again? Are people willing to keep a person hooked up, de facto alive, for an infinite period, or until the money runs out?