I thought it’d be interesting if npcs saw a corpse/ragdoll of their own kind (Or any kind, if that’s not possible,), they’d attempt to avoid it, or take a different path to reach their destination/target. After watching three combine soldiers die trying to go through one door, wouldn’t it make sense that the fourth soldier would try a different door or path instead?
Another thing, which I know I’ve seen before somewhere, but wouldn’t know how to create, is a code that’d Make npcs approach something if they hear it make a noise. Making zombies-or anything- attracted to the sound of gunfire (or away from it, if they’re unarmed…Again, if that’s possible,) would make things more interesting.
If either of them are possible, npc battles might seem a bit more realistic.