It's a hard question. I think for all practical purposes, when someone is on their death bed, body shut down and just about flatlining on brain activity, it's time to pull the plug. No one would want to live in such a state, kept alive indefinitely by machines when there is no hope to return to a normal life.

I have an issue with your tern 'human animal' I understand what you are trying to convey but I believe it is misconception and misinform us about who animals are. Animals are not pure instinctual beings like we believed 50 years ago. there is overwhelming evidence that they are sentient and far more complex then originally believed.

Also I work with people who have Dementia as I am in medicine They are self aware. Self awareness is not their problem. They have problem perceiving their surroundings, or processing information about their environment.

Let's see if I still remember some of this stuff. Reflexes come from the spinal column and are a part of the somatic nervous system. Like the autonomic nervous system, it can still operate although brain function in the cerebrum has ceased. A person can be vegetative or brain dead with the autonomic and somatic still functioning. Thought, being self aware, being sentient, whatever you want to call it, comes from cerebrum. Is that a human animal? No, an animal would still have basic instincts. Vegetation and brain death doesn't have basic instincts.

Severe dementia, actually late stage dementia and alzheimer's show brain degradation. Plaque build up is so severe that at late stage cognitive function ceases and the brain dies off with only the somatic and autonomic functioning.