Is It Even Still Possible (The Rejoining)

[Slatersev]

This question was actually answered in the Final Role Quest that unlocks after you complete the 4 Role Quest lines.

TLDR: The Ascians had plans to restore the 13th using the 1'st over abundance of Light Aether, Ardbert and co naturally ended up derailing the plan quite thoroughly.

[Brightamethyst]

TLDR: The Ascians had plans to restore the 13th using the 1'st over abundance of Light Aether

No they didn't. That was just a lie they told Cylva to trick her into helping prime the First for rejoining.

[Jandor]

TLDR: The Ascians had plans to restore the 13th using the 1'st over abundance of Light Aether, Ardbert and co naturally ended up derailing the plan quite thoroughly.

We know that wasn't the Ascians real plan because they successfully executed their actual plan and used that Light Aether to rejoin the 1st to the Source. We had a lot of quests about it

[YianKutku]

This question was actually answered in the Final Role Quest that unlocks after you complete the 4 Role Quest lines.

TLDR: The Ascians had plans to restore the 13th using the 1'st over abundance of Light Aether, Ardbert and co naturally ended up derailing the plan quite thoroughly.

The issue is that as Cylva tells it, she uses the same type of wording that Ascians generally use (possibly quoting them verbatim), which is very probably deliberately worded to be as vague as possible.

The actual words used:

A shard subsumed by Dark demands a mirror of blinding Light. Primordial forces will strive to achieve equilibrium.

This just states blandly that if X happens, then Y will also happen. It doesn't actually say that X will cause Y. Therefore, the Thirteenth falling into Darkness doesn't actually mean the First falling to Light has anything to do with saving it. A common interpretation on this forum is that the Thirteenth falling to Darkness just meant the First was affected by it, and thus made easier to fall to Light, and Cylva was doing the Ascians' plans because she thought it was the best way to save the First, while assuming that the Thirteenth is forever doomed.

In fact, the extra questline with Unukalhai in 5.4 revealed that Cylva didn't think the Thirteenth was salvageable, and that the Ascians didn't think so either (according to her). It was only the (ongoing slow) reversal of the Empty via Eden that helped convince her and Unukalhai of the possibility of doing the same to the Thirteenth.