I have an idea. Since the Korosu are already not a part of the Espada maybe they could do their own thing for a while and if it suits the members of the group then maybe they and some of the soul reapers can band together to stop the threat f the Espada. Because the way I see it, Korosu don't like the Espada and the Soul Reapers don't like them either. So, the enemy of my enemy is my friend