The first question we have to answer is, do we want to stop Hermes from creating and sending out the Meteia? Or do we want to figure out how to kill Endsinger without the sundering?

For the first option, we could build another time machine, go back even further in time and convince Hermes to change the Meteia's mission a little bit so they didn't get overwhelmed when they discover a dying star. Or maybe show Meteion the aftermath of our battle with Endsinger and show both Hermes and Meteion that everything will be fine, there is hope in the future and he didn't need to send out the Meteia to ask such deep philosophical questions to various life forms. The timeline would branch, both civilizations survive.

For the second option, we could convince Venat to share the upcoming Final Days with the Convocation and also gave them a better solution. Instead of summoning Zodiark to shield the planet with Aether to block out Endsinger's song (which would only be a temporary solution and lead up to the sundering as in our timeline), summon a primal of Dynamis filled with positive emotions to do battle with Endsinger. Venat put a tracker so they could easily find her nest.