Agreed - I was hoping that one of them would finish Mesaana off. Well, the reason they might still be alive are that they were ordered to cause maximum damage. In the midst of a huge battle in which their lives are already forfeit, it might be easier to kill big numbers of channelers or important targets by waiting until everyone's actually settled down and dropped their guard. During the battle and right after, everyone's on their toes - in two days, they could sneak into the rooms of all the sleeping novices and take them out.

Also, BSand made a point of telling us that the rings could be removed after being worn, and that doing so would extend the life of the wearer by a days.