A kitten jumped on my head right then, but I woke up thinking about this very common fictional trope. Mine was dressed in up in Web 2.0 sci-fi pop culture drag, but there's a very similar scene in Lord of the Rings, among many, many others. As I got up and checked the snow (about 10 inches) it was in my mind as pipe dream nonsense, wish fulfilment for those left holding a breathing corpse.
But then I remembered S, a childhood friend who really did wake up three weeks (or was it a month and a half?) after a car accident. Obviously this is only true some of the time, and there's a raft of problems, and the better your medical intervention is the more likely it is you'll be able to save the person, and they may not come back the same, but there's a basic lesson in the story; before you give up on someone, find a person who knows what they're doing, ask them if anything can be done, and wait.