I know it's been said that Nihilis and the Exile were designed to be mirror opposites of eachother, but I personally think it goes deeper to the point that Nihilis and the Exile had the exact same connectivity to their fellow soldiers and jedi. So, while the Exile dealt with the trauma of the Mass Shadow Generator by cutting themselves off, Nihilis used it to survive the detonation and possible exposure to the vacuum of space. The Exile is also the one answer to Nihilis' endless hunger as it is impossible to absorb something that is no longer there or more accurately something that has effectively become its antimatter. So if one subscribes to the Unifying Force theory, it had a hand in creating Nihilis, but also created the Exile to cancel him out. (also as an aside, it'd have been pretty awesome to see the Exile use a visual effect when they defeat Nihilis like an accretion disk from a Black Hole that envelops then annihliates him until his empty mask lands on the ground where he once stood)
I can understand why Kreia was so adamant about destroying the Force, but it makes me wonder if it might have found some way to stop her anyway. (Though I guess technically it does since the player can't actually agree to go through with her plan)