IIRC the “Fallen” in Diablo 2 would sometimes run away. This is sort of funny because they actually did have a type of guy that could revive them.

I think the Grunts in Halo would run too.

Mostly it seems to be treated as a gimmick or joke in FPS and RPG. Individual enemy AI is usually pretty bad in these genres, so they probably just don’t have the capacity to act smart enough to act scared.

Of course, it’s a main feature in some tactical games, like the Total War series. That’s more of an explicit mechanic though.