Horrified by his own creation, Aarau created a final precaution should the worst come to pass.

After successfully casting the spell you maintain concentration, with advantage on concentration saves. Should an undoing of reality happen such as, the destruction of the casters plane, Crystal Sphere, or universe happen, while concentration is maintained on the spell, a sphere with a radius of 77 feet or diameter of ~155 feet, centered on the caster, is turned into a demiplane which survives the surrounding destruction. The spell doesn't create a demiplane itself, instead preserving an area which becomes a demiplane when the rest of reality is carved away. At this point the spell's effects are permanent and the caster may break concentration.

The demiplane preserves everything within it, the edges emit an even sun-like light that can be temporarily turned off by the caster, once the caster dies this control passes to their closest living blood relative, if there are multiple equally close relatives, the one most genetically similar to the previous controller of the light is the inheritor. Plants grow 7 times as fast and always produce bountiful harvests,there is minimal rot and decay. The ceiling of the bubble will sometimes produce heavy rains, and when water evaporates within the demiplane it ceases to exist, resulting in a fairly constant water supply. The shell is solid and perfectly smooth, and it maintains a constant temperature of 57°f. The shell has a shimmering, flowing, and slightly translucent appearance, and is sky blue during the “day” and pitch black during the “night”. Magic still functions within the bubble as it did before the catastrophe.

Upon the creation of the demiplane, a demiplane replica of the outer plane which most closely aligns with the casters alignment, also with a 77 feet radius, if the caster has a neutral alignment the plane resembles the astral plane. Within that demiplane exists any combination of creatures native to that plane with a total CR up to 21, the caster doesn't get to choose these creatures. Additionally within that plane exists a demigod fragment of the god the caster is most devout to, or another god of the casters choice, this demigod is much less powerful but functions similarly to how it did before granting divine powers to clerics and paladins. All souls that would pass on to an afterlife in the outer planes within the main demiplane go there, regardless of alignment and the 2 planes are largely separate but can be traversed between via standard methods. No other plane can be accessed from these planes. These effects dont apply if the spell is activated within the outer planes or the astral plane.

If anything exists, it's possible the demiplane may collide with it after an indeterminate amount of time, be it days, decades, or millennium, at which point the inhabitants of the demiplane will be released into the wider world. If 2 of these bubbles collide they will “stick together” and join at the sides, opening up where they touch. If the 2 bubbles are at different angles they maintain their separate gravitational alignments. The outerplanar demiplanes will assume positions resembling their positions on the great wheel and souls within the bubbles will go to the plane which they most closely align with, if the bubbles have an overlap in the outerplanar demiplanes, they will form different layers of the plane.

If the effects of the world ending spell demands that the DM surrender control, they can continue the campaign within the demiplane.

If you gaze hard enough through the shell of the bubble, you can begin to make out the horrors that exist beyond existence, separated only by a thin shell. It's best not to dwell on them as you wait, imprisoned, within, what could be, the last bastion of a forever lost world.