What do you think it will be/involve?

This is kinda a weird theory, but I imagine that what happens is the Aedra spokes detatch from the mundus, and mortals are left to support the world on their own. Because the spokes are gone, mundus (the "land") becomes detatched from the rest of the Arubis ("falls"). Those that live "above land" are trying to re-connect with the Arubis, while those who live "below ground" are trying to move away from the arubis, and towards the psijic endeavor. Really though, this is all based on just one of a thousand possible interpretations of the words "land" and "fall"