I really love the rocky jagged terrain of Stonefalls, and I especially enjoy pulling mobs next to a cliff and them knocking them over the edge. But they do not seem to suffer any falling damage. If it's high up enough they scream as they fall but they don't seem to take any damage. When I jump from that same height I certainly suffer damage. Another example, when I was in Emberflint mine I knocked a human mage into a lava pool and I just sat there and watched her health as she cast spells at me, If the lava was doing damage to her I wasn't able to tell.
If mobs really don't suffer any damage from the environment, whether it's falling from a great height or being pushed into lava that would be a little disappointing.