Once they are reformed, they leech all of the heat and energy from countless worlds and concentrate it in a single reality.  The energy boils the oceans of silt-choked waters, disintegrates the landmasses.
Their bodies form into a large, complex shape, with only small fragments in this one world.  The extensions of those same fragments extend into other realms, in concentrated, specific shapes, made for a purpose: to survive the next step.
The energy is released, and the planet shatters.
The shattering is so extreme that it extends into other worlds, through the same channels that the fragments used to extend into other realities.  Every single one of the remaining habitable worlds is destroyed in the ensuing blast.
And the fragments radiate outwards, shedding and dropping their protective shells as they sail into the black, empty void.

Worm Interlude 26