The UN has only a status as observer. That´s not a mandate to provide security in the region.
When Israel has cleaned the area from Hizbollah, NATO can control south Lebanon so that the terrorists won´t come back. Of course, it´s not NATO´s task to eliminate Hizbollah.
The UN has been borderline hostile to Israel and the United States in their complicancy with terrorists. We can thank the Lord for the good work of Ambassador Bolten as he looks after US interests in that vipers nest.
Whether or not NATO will provide a buffer on Israel's northern border is to be seen. I think that if it does, that will draw the terrorists to attack them so they better be ready to fight.