Well, I'm actually the one who happened to bring up the falling in a river and losing a pack thing. I brought it up because it did happen, though it wasn't as severe as completely losing the pack. We were crossing a fairly wide xreek and the middle guy somehow lost his balance and went clear under. He said he bailed his pack because he couldn't right himself right away in the current.

He got out of the river just fine after that, soaked but fine. His pack only went about 50 yards before it got snagged going around the bend on a tree that had fallen in the river, lucky for him since that was a lot of money being rushed down the river. His lighter didn't work for a while and all of his stuff was pretty soaked, but he could have just as easily lost it all. We had enough gear to finish the hike, feed him and keep him warm, but it did happen. It wasn't really a scare since it happened quickly and I didn't see it until I saw a pack floating down the river as I turned around on the opposite bank. The other guy was still on the other bank relieving himself so he was totally clueless until he popped out of the alders a minute later.

It isn't like it happens a lot obviously, but it isn't like it doesn't ever.