Maybe the Sundering isn’t WOL/Azem dependent? If Azem is staying out of the Venat/Zodiark fight - then maybe someone else is the person who actually instigates the Sundering - or works with Venat to bring it about?

My guess would be “Mr Hard Decision” himself, Urianger. I suspect he (or someone like him) is going to fill out the Cylva role - but from our group this time. (Writers love echoing previous stories). Urianger might travel to another world/time/timeline to go cause trouble over there. I could see him easily taking up the mantle of this “most grievous matter” to go help Venat cause the Sundering.

There’s still time for something like this to happen in both of your timelines - both our prime one, and the “G” one.