I fell off a bluff on an IMBA epic trail where the path went RIGHT to the edge of a (small) cliff beside the lake. There are names of sections with cute little signs, such as Post Rock, where they have upright limestone in sections like fence posts.
The section I fell in is called Bike Wash.
There are a few places you could fall all the way to the water, but a sandy beach is more likely. I fell about 4 feet below the trail into a nook and the bike was on top of me. Since I had a riding buddy, I just waited for him to look back and see the upside-down bike and bail me out. It would've been pretty tricky to get out on my own, but doable.
Nothing worse than bruises because I was wearing protective gear: knee and elbow pads, helmet, gloves. I don't wear the knee & elbow pads on easier trails, but for downhill and any rocky singletrack I wouldn't go without. If it's fast and rocky, I wear a full-face helmet.