So I discovered this by accident, I was pushed out of Twin Peaks by a shaman. In my attempts at jumping back with the Demonic Leap ability I have as a Demonology warlock, I failed because I was already too far out on the hillside. This is the place where the river running from horde base down outside the map. Check screenshot below.
Because I was too far out when I leaped my way in, combined with the fact that I was currently using the "Glyph of Falling Meteor"
Glyph of Falling Meteor - Spell - World of Warcraft
I ended up going as a meteor all the way down to the bottom of the pit. Screenshow below.
https://i.imgur.com/I6HEL.jpg
Down here I was basically invulnerable, because nobody else can get there, so going here with the flag might be a good idea if you are loosing a BG; and all you want to do is piss off the opposite faction.
I was able to move around down there, but 1) My camera was still stuck up there, and 2) There was a wall where the river closes in a bit, so I could not get out of the arena drawn on the map.
Unfortunatley I was not able to perform extensive testing, but this might have some potential, considering there are several places where you die from falling down, and I might be able to get out of the BG if i find a hole in the air wall covering the Twin Peaks river.