Universal Rule.
At the end of a phase, if there are no friendly models with Chosen of Ashuruk or Opportunist on the Battlefield, immediately remove all your Orc Slaves models as casualties.

At the start of a friendly Player Turn, if there aren't any friendly units with Chosen of Ashuruk or Opportunist within 6" of an unengaged non-Fleeing Orc Slave unit, roll a D6:
1-2: The Orc Slave unit immediately flees directly towards the nearest Board Edge.
3-4: The Orc Slave unit is Shaken until the end of the Player Turn.
5-6: No effect. The Orc Slave unit behaves normally.