The relic helm of The Godless will be your reward for completing all jobs in the emissaries activity.
If you lose this helm you can reclaim it from Holstein for 80,000 coins.
You can change your faction to The Godless at any time by speaking to Holstein, and this will not reset any progress made in the activity. If you have claimed a helm from another emissary, this will be removed from where it is stored upon changing your faction. You can then reclaim one that represents The Godless for free by asking Holstein about it.