I've noticed that I can fall a fair distance without taking damage, but I've never fallen any farther than I could survive. If you fall far enough is it possible to take damage, or is falling damage just not accounted for? Are there kill zones if you fall off the map or into unreachable areas?
No, falling never causes damage. However, there are places that result in insta-death if you fall there.
One good way to tell a fall will result in death is to pay attention to the map. If your destination falls outside the boundaries of the map, odds are you wont survive the journey.