You geniuses do realize this has nothing to do with ISIS, right?
ISIS is hundreds of kilometers away. The rebels in question here are Jabhat al-Nusra. They also originally stemmed from Al-Qaeda in Iraq, but they are mortal enemies of ISIS.
Right now, ISIS is confined to the north-eastern corner of Syria while Jabhat al-Nusra works mostly in the south-west, so they pretty much steer clear of each other. But they have fought each other before and they may do so again. They are certainly no allies and they are not to be confused with each other.
As for the situation in question, it should be noted the UN commander did negotiate a deal which should have allowed the UN to free both the Fijian and the Filipino peacekeepers. Unfortunately, the deal fell through because the Filipinos defied orders. Now the Filipinos got away but the Fijians are still stuck.
I'm not necessarily saying that the UN commander made the right call. But I am saying that I don't know the full details of the situation and I do not understand the intricacies involved, and therefore I am not qualified to pass judgment. Since nobody in this thread seems to even know which rebels are involved, I'd guess none of you are qualified to pass judgment either.