User blog comment:Valarian of Naples/The Final Day: A suggestion-run story of the Star Saints Space Marine Chapter/@comment-5691049-20141102173826/@comment-5691049-20141102183931

In order to sum up the new backstory, Captain Erasmus Vurne has been sent on a death oath for abandoning Imperial Civilians to the "mercy" of the Dark Eldar, alongside the four squads that had been defending the innocent when he gave the order. Though this decision ultimately allowed the Star Saints to secure their victory, Erasmus and the four squads were sent to banish the daemon prince known as Kresh'har the Slaughterer as part of their death oath. Without support, the small band of exiles must fight their way through a daemon world if they are to ever return to their chapter.

On a side note, Ang'mar will still be an artificial world, only it won't have the whole offline gellar field explaination.