any model with the Zombie Master skill can take over and command an Undead Legionnaire squad that has lost it's original leader....
until that time, the ULs just lose one action, but they get that back if taken over by another model...
that's why, under the listing of the Undead Legionnaire, there are 2 models that have the Zombie Master skill, the Necromutant leader and the Curator, who then can take over the squad if need be...
B...