I will add that there is probably no way we can know when there is a 0% chance of saving a position. A hopeless situation in the truest sense, I can never know about, as I don't know when a one in a million hallucination may occur. Again though, it should all be up to the player; the resigner should be considering his time spent, not his opponent's. Never knowing for absolute sure what the result will be until it happens is part of what makes chess competition intense in my opinion.
Competition is a fierce animal but it's like a specific phase a person is in. They can act in a way that is completely separate from what they do on the board.
Resigning is the right thing to do when you are in a hopeless position, Chess is the challenge fo two minds not a game of destruction!
Unless of course You think there is a chance that your opponent will drop dead of a heart attack and you can win by default!