So my players are knee-deep in a full on invasion by a warband led by a Dark Apostle of the Word Bearers. The invasion is in its middle stage: traitor guard and cultists lead slave gangs of captured and converted civilians to build great artifices to Chaos. Defilers, while not directly engaged, have been seen scurrying through the rubble of the urban war zones. Apart from his late stage goal of a limited release of some daemons, what would be some things a Dark Apostle would be leading his human hosts to be doing, besides what I've mentioned already?

For clarification, I say its middle stage because the Imperial Guard is cut off from reinforcements elsewhere in the system by a naval blockade and units down to individual squads are scattered and usually pinned down throughout the once cosmopolitan planet.

Massive Sacrifice, finding a relic (big one for Word Bearers, they love books by Lorgar), converting more people to chaos.

You could go for a twist. Instead of finding a relic important to them, it could be either a relic of the Imperium or a relic of a rival chaos god/gang which they are trying to find/defile in time...(how to defile a nurgle relic? Hmmmmm, have 50 sisters of battle scrub it clean?)

Or they could just want to create a warp storm to cut off the planet/system from the rest of the galaxy.

Or have it sucked into the warp so it will be spit out in a deamon realm, showing how worthy the dark apostle is....

What about converting the citizens that are left on the planet to chaos worshipers? If I remember correctly, the dark heresy books talk about how the word bearers would stay many months after compliance to ensure the populace was correctly taught and venerated the Emperor as a god. Maybe the Dark Apostle was from the heresy time or was instructed by one from that time and the mantle has passed to him?

Well this Apostle, Crixus, is already hard at work converting. He's converted most of the survivng civilians. He turned most of the PDF and newly tithed Imperial Guard regimemts right off the bat.

I hadn't thought about a warp storm to cut it off. His warfleet can only last so long before the Imperial Navy wrecks it and drops a million guardsmen dirtside. That might be a good one, and would fit what he's already doing. Just need to build more monuments and maybe sacrifice a bunch of people (those converted civilians come to mind) and boom, warp storm.

Thanks for the ideas guys! Good stuff!