I still think the maw may be the literal mouth of the forked serpent… but Im a bit crazy about that.
THE END OF ALL THINGS
The crooked serpent with no eyes is watching from the endless sky.
Forked tongues flicker through the black pits in dead stars.
The veil between dream and dreamer slides away like skin from bone.
And even the darkness howls for the light it once despised.
They could have simply have been dumped there in eternal sleep. The only Souls that would fade from existence would be Souls dumped in by Revendreth and that’s due to being utterly drained of Anima.
Of course that begs the question: are Souls just floating in an empty abyss doing nothing stuck in eternal sleep any different a fate from your idea of Souls utterly unmade?
I always phantazised that the maw was the original shadowlands where the devourers ate all the souls, feeding into Azeroth.
Then the first ones came and created the big cycle and created everything we know today.