Uniting would severely undermine Ember's leadership. I'm sure all the elves would survive just fine united, food isn't a problem, but Cutter split the tribe for a reason...unless they plan to stay together permanently, it would be detrimental to unite the tribes for very long. That doesn't mean Ember's tribe has to live next door to Angrif. The Palace can take them all over Abode...they could settle on the other side of the world. The real conflict is, with how quickly humans breed and spread, how long before Ember's tribe finds themselves in the same situation and have to be spirited off to some other part of the world?