I think if the person lingers on the edge that what matters most is calming their fears and not letting them feel the throes of death. If they come back, then good. I'd not want to feel fear and pain and would rather fall asleep. Most likely I won't get to die that way, but I have seen a peaceful death aided by morphine. I'd want to go that way even if the morphine introduced a bit more risk that I might die sooner. I'd want family near by talking to me, perhaps stroking my head, perhaps some ice cream in my mouth, perhaps a gentle breeze and pleasant sounds. They could remember me smiling on my way out.