It's also worth noting (not that I'm defending anyone or taking sides) that when running in a group in poor weather, unless you're the one at the back it can be quite hard to make sure nobody is dropping behind. It may be that this bloke was struggling coming off the hill and stopped for a moment for some reason and was unable to keep up. If he was hypothermic he may well have got turned around and headed back the wrong way, hence the sudden apparent gap between him and his group. This isn't excusing the fact that the group split, but simply pointing out how fast it could have happened. Without knowing the facts it's difficult to properly judge the situation so it's best left to those in the know. I'm sure DB and team learnt a lesson from it, and thankfully the guy was ok.