When The Scarlet Witch replaced Earth-616 with The House of M reality she accidentally tore open a rift in time and space and unleashed a wave of chaotic temporal energies that slammed into countless alternate realities, breaking down the barriers between Universes and causing untold destruction wherever it went. The Chaos Wave eventually washed up onto The Starlight Citadel and crushed it killing Roma in the process who, despite all her power, was unable to hold it back.
Having regained their memories back almost all of the original members of Excalibur banded together once more and sought to desperately find some way of stopping the Chaos Wave before it destroyed all of Creation which they did in the end but at the cost of Meggan
, Captain Britain's
wife, who merged with the rift and in turn all of reality in order to undo the damage caused by The Chaos Wave. It should also be noted that The Chaos Wave was responsible for the resurrection of Mad Jim Jaspers