I haven't fallen off the world yet... but I've witnessed a guildie of mine do it.
We were farming mana motes from the mana things in netherstorm. She wasn't level 70 yet, so had to go around the rock formations to get to me. Anyway, I flew up over a cliff, she went around and fell into a hole
Speaking of Netherstorm and falling... does anyone have that Rocket Helmet that was a reward from saving Area 52 from the fel reaver? If you do, it may interest you to know that it can be used while falling, so if you time it right you can launch yourself up into the air while falling, gain the parachute buff, and float down to safety. Keep in mind that the parachute only lasts a few seconds, so if you use the helmet at a lethal height, you're still going to die when the parachute runs out.
I do this all the time when dealing with Aldor rise. If I just missed the elevator, or I'm just in an impatient mood, I'll toss on my rocket helmet and take a dive
(Though... a few times I lagged and the rocket helmet didn't activate until I hit the ground >.>)