The Firseid Sandbox
The Great Phoenix of the Desert provided the party with the details of a ritual that would forever sever Firseid’s plane from others, cutting it off from magic for eternity. Magical creatures (including the swarms) would wither and fade from the world, and even the most powerful extra planar creatures could never again trouble the world. The souls of the dead would evaporate rather than make a journey to the outer planes, and the gods would cease to influence the world.
It’s incredibly drastic, and the party immediately balked at the idea, but the phoenix provided the following instructions:
Take the Meteor Heart to a place of powerful wild magic, a place where the boundary between planes is weak and powerful elemental forces capable of destroying the Heart exist. There are a limited number of places like that in the world, but they do exist: places of grinding ice in the far north, volcanoes, earthquake faults, and mountain tops buffeted by the four winds at once. The orb will shatter and its essence will permeate the world, driving magic from all corners and severing the connection with the planes.