[Draenin]

If the NPC is being blocked, have it return to its former position. If the returning takes more than, say, 5 seconds, make it instantly return to its place. Also, the enemy should return to its place after the player is out of its range of sight for a certain amount of time as well. Nothing on Zodiac really blocks except for players and scenery / NPCs, so checking for whether or not the NPC is being blocked for a certain amount of time should be fairly simple.

It's just like if you were running away from a monster and back into a castle town via a drawbridge. Once the Portcullis Gate closes, the monster wouldn't keep trying to pursue you through a grid gate made of iron.