I wouldn't say I've come that close, but on two winter climbs in the White Mountains, I saw that as a real possibility if fate, luck, or whatever else you choose to call it had changed a couple of degrees against me. Once, I simply bonked about two hours above three line and pretty much had to rely on my partner moving me down the mountain until we were no longer exposed. The second time, we got caught in white out conditions and actually got seperated for a few moments and I returned the favour by going back up to giude him back down to safety. Thing is, the mountians can screw you up really quickly , and before you know it, you're in a situation that could turn bad just like that. It could be as simple as having your goggles icing over in 70mile winds. You can't see anymore and now you're in it. I don't think it is always something spetacular that has to occur in unforgiving conditions, just enought to take you off your game.