How is the world broken by this change?

Astrology is harder.

Sidereals have to spin fate directly. Or at least *can* spin fate directly.

The Maidens no longer curtail the Spiders' hate. Paradox is more of a problem.

New Stars cannot be made.

Creation is crumbling, one mile of radius per day. In thirty thousand days, Creation will cease to be.

Heaven is separating, one gate closing per week. In sixty weeks, Creation will cease to be.

See the Discworld novel "Reaper Man."

Life gets weird. Instead of things falling down, they fall up. Then they turn into fifty pumpkins.

More fate/reality breakages, starting small but then growing. Beings from outside creation use the opportunity to slip in.

All the normal suckage of the age of sorrows is happening (Solars, Empress disappearing, etc), but it's because the fate-planning system is fvcked.

New (i.e., reincarnated) Sidereals can't be made.

The Unconquered Sun decides he needs to take a more hands-on, proactive managerial approach to Heaven in the Maidens' absence.