system
Given the following post, respond as if you're commenting on Reddit:
human
[Warhammer 40K] The Imperium had made it possible for the Atronomicon to be lit using only the power of sacrificed psykers in roughly the same numbers used now. Then the Emperor dies. How does Imperium fare?
gpt
Bad shit still happens. 
The Emperor is holding back the broken Webway gate below Terra, and if he were to expire, the infernal portal would break open, letting in countless hordes of daemons right inside the Imperium's capital. It's also theorized that the portal wouldn't just break open, but would also grow in size, possibly becoming a Warp Rift that swallows all of the Sol System. 

TL;DR: The Carrion-Lord of Mankind may not be a God, but he's vitally important to humanity's survival, whether he's fueling the Astronomicon or not.