The five meteors hurling towards the battlefield is seen by every player on both sides. There was one thing that all entered their minds and it is that they are all going to die. Three of the falling meteors were cast by the Arch Lich itself which is why it is hurtling faster than the other two.
It seems that the meteor would cover the whole area of the battlefield regardless of their alignment which made some of the undead players following the Arch Lich flee from the battlefield but that became their fatal mistake. The players that were turned to undead in the Arch Lich' faction now knows that they chose wrong in choosing a side.
The undead players from the Arch Lich' faction is not able to run away from the battle not because they should not but rather they could not. The undead players of the Arch Lich now felt that the pledge that they uttered back then was not just a mere oath but the spell required for Perfect Servitude.