Interesting Question Regarding Voidsent.....

[Cleretic]

The Ascians considered the Thirteenth a lost cause because there was no way to bring it back into balance. On the First we brought back some of the balance not by injecting darkness, but by removing some of the excess light. That's not possible on the Thirteenth because there is no (or at least not enough) light left so removing some of the darkness wouldn't change anything.

Though that conclusion is now in doubt, after certain ShB revelations...

Their plan was to, once Zodiark was together enough to be operable, sacrifice lives to Zodiark to fix the Thirteenth, then do a proper Rejoining. Because of course that was their plan, it's always their plan even if alternatives are available. If Lahabrea was out of peanut butter his first angle would be to sacrifice lives to Zodiark to get more, he'd only settle for alternatives once that proved unviable.

And while completely unrelated to the topic, it's folly to consider a 'non-cataclysmic Rejoining', because a Rejoining by nature requires a destruction of a society, even if doesn't cause an apocalyse on the Source. A 'non-cataclysmic Rejoining of the Thirteenth' would still effectively kill the Thirteenth, and to no real benefit unless you're specifically an Ascian who considers all sundered lives inferior to unsundered lives.