Often the hostiles won't make that leap. In fact, I had a spider that wouldn't drop into a 2-deep hole when I was on the other side and up 1. But then, I've also had one repeatedly climb a hill away from me then jump back down trying to reach me.
If the just happen to be jumping around, they can in fact fall off, just as any other mob will do. Also, b/c mobs have the same amount of health as you, judge how far it takes for you to die and compare it to any situation.
While chasing, mobs sometimes will jump off, but sometimes they just stop. I've noticed this a lot with creepers and skeles.