Elemental and undead units

[Kylix]

I think that in all the campaigns, when the undead leader is defeated, all its undead units should die as well. The only campaign in which this happens is UTBS, where, inconsistently, also bats and dark adepts died after their captain's defeat. For the elementals, I only remember Caladon controlling the Fire Guardians (a thing that should have happened also to the merfolk once taking the Fire Sword), but they also didn't fade away after their leader's demise.