In my game, I would give the magician the EP for casting the spell, plus EP for the kills. However, the kills would be reduced because the targets were unconscious. (I don't recall if that's in RMSS, but I'd use something like 1/10th normal KP.)
If someone else had gone through doing the kills, I would still give the magician Idea Points - again, don't remember if this is in RMSS, but in RM2, that would=1/2 the experience that resulted from the idea of sleeping the enemies. (That does not reduce the experience the others got.)