I was toying around with Sneak and noticed enemies just stop and stay where they are once they lose track of you. I think it would be cool to have some variety to an enemies behavior after they give up the chase.
For example: if you ditch a rat, it'll wait a bit before randomly pick a spot nearby to pathfind towards to simulate searching, then repeat. If you're lucky, they'll be facing away from you to let you sneak past or get a chance to backstab, or maybe they'll wander into another enemy to fight. They probably shouldn't stray too far from where they stopped to make re-engagement more predictable and in-fighting less likely.
Taking the idea further, it might be cool if more intelligent creatures like knights eventually nav'd back to where they first spawned to guard their area.