Regardless for the sake of everyone else we had the example, from Halo (2?), of the enemies running away when the "elite" mob was killed. The initial intention was to make the mobs seem smart, like they had morale, but in testing people kept on reporting it as a bug, even after you added graphics and voice overs to signify why they were running away.
Totally. And you have no idea how frustrating it was. The leadership model in Halo 3 was pretty complex; leaders would absorb nearby units, if a leader died the nearby units would break, they had various complex behaviours, they would eventually gain their confidence and start attacking again. But ultimately, even when it was telegraphed well, it just wasn't as fun as it should be.
State changes in an encounter need to be big, well telegraphed and repeatable. If a Grunt kamikazes you (runs at you screaming with lit plasma grenades held high) 10% of the time that you kill the leader, the player will virtually never see it, he will die randomly, he'll get frustrated, and quit playing. So we cranked it up to 50% of the time, and now we got people saying "why didn't a Grunt kamikaze me? did I not kill the leader? shit, where's the leader?"
So we made it 100% of the time, and it's still my favourite AI behaviour to date (and I whipped it up in like an hour; the code is horrible).