This is a thing that should be present in all games of this type, and really I would encourage every GM to take this lesson to heart in tabletop.
Amen. I understand situations like spider lair. You're invading her domain. Fight to the death. But I don't get the tieflings.
Again, most fights are fine, but I do like Drath and RagnarokCzD suggestion about the boss goblin shooting deserters. That's fun right there.
Other fights where fleeing Enemies make sense:
1. Zhents in Defiled Temple. Cultists ain't their fight. If you killed Gut, etc., they might fight a bit but then get the flip out of there.
2. Goblin cook. Fighting starts, she runs arms flailing.
3. Loviatar priest. Like Zhents, not his business. No reason to fight.
4. During the 30 goblins camp fight after killing the leaders, because no leaders, those not branded just start to flee. The crazy branded stay because they're zealots. They fight to the death.
5. Wind mill - oh wait! That already does exactly what I'm talking about. Hit the leader and the others retreat.
Again. Not every fight or even most fights because that would be boring, but where it makes sense.
