Something I've been thinking about that could ad some drama in a Warhammer roleplay or warhammer themed D&D game is an npc who was once a Chaos worshipper until thet willfully and without deception, turned away from it. After all, the 4 dark gods favor humans because they choose to worship Chaos. But choice is a two-way thing. What if someone abandoned Chaos for some reason? It would likely only be possible in early stages of Chaos worship, before the mutations show up and the 4 gods gain dominion over your soul.