Spoilers for Nod-krai Act 7 and 8. It's revealed that Rerir along side the ghost of Tholindis, they are forever trapped in the moon's reflection inside the moon gate. It essential acts as an eternal prison for his actions in the genocide of the people of the crimson moon dynasty, which included several uninvolved innocent men, women and children. It's also revealed that the Abyss was largely responsible for driving Rerir to become what he is now, and ramming up his emotions which is something the Abyss is known to do, just like with Apep. Preying on your weakness and driving you to anger. Now, he's gain clarity of mind, with the Abyss no longer controling him. But, however tragic Rerir's backstory is, he still killed people and being trapped forever with no escape feels like the perfect punishment for him.

The most tragic character in all of this is Tholindis, who was also controlled by the Abyss, and in conformed to be long dead after going through the moon gate. Only an afterimage, a ghost is left in the moon's reflection, with Rerir acknowledging that she's already gone.

I really think this is the best possible conclusion to Rerir's story, a perfect punishment, cuz anything less after what he did would be very divisive.
A good conclusion his story and punishment for his actions.