Complex sentence: The three additional members have been sent by their various organizations to observe Haruhi and prevent these powers from being unleashed, leaving to Kyon the task of maintaining for Haruhi the illusion of a normal life.
Split into simpler sentences: The three additional members have been sent by their various organizations to observe Haruhi and prevent these powers from being unleashed. This leaves Kyon the task of maintaining for Haruhi the illusion of a normal life.