We killed Emet-Selch by using the corrupted Light aether of the Lightwardens against him.

And it was a lot of it, so it's probable that our act against the Sin Eater and the disappearand of the Lightwardens Light aether restored the balance between Light and Dark enough to prevent a Rejoining, Emet-Selch death or not. But the First is, even now, in a preocupying state, just not as much as before.

It's Ryne and Eden that will restore the balance between Light and Dark, and all other elements with a more durable effect.