What a fortunate end to an extremely careless mishap. You truly got away with one ... THIS time. My question is when standing outdoors in a rocky environment why would you not take every imaginable precaution to eliminate the likelihood of such a disaster from occurring?
For Pete's sake everybody, put your gear on something stable while changing out lenses! If you can't find a flat spot with enough room to work, SIT DOWN and put your gear in your lap.