The death of a Third Circle, for that matter, is probably going to be an Event. They don’t tend to die soft quiet deaths like a human passing away in his bed. The death throes of a Primordial soul is going to be a miniature cataclysm all its own, especially when you perma-kill it.
I guess I just treat Third Circles as more important than most people, I suppose. In my game, if you shiv Erembour in the back you’ve just destroyed a Thing That Will Never Be Again. You have lessened the world, removed one of its wonders and terrors. You have put a crack in the body of the titans who forged existence from chaos. Her black blood will spill across the ground and her moaning servants will shriek and tear themselves apart in fits of agony and despair and each of her subsouls will shudder and collapse as Alvuea and her brothers and sisters perish in horrible agony and then the world knows that from that moment forward there will be no more treasures from the Forge of Night, no new demons spawned from their subsouls.
You have broken the world in your arrogance. Maybe not a pleasant part of the world, but still a part of it. You have accomplished a Legend, which they will speak of for many generations. The Underworld will remember.