well the thing is they found a new home world after they declared traitors and their previous home was destroyed after they declared exterminatus upon it but there is more than one catch. The world they recruited from happened to be in reality..... a deamon world which was made to appear to be a death world which also happened to not only be inhabited by abhumans entirely in addition said world was controled by a warp deity which happened to be a fragment of tzeentch which all four of the races of abhumans had their souls owned by her and the worse part if their blood gets into the system of any human or even astartes it will begin to alter their brains and make their souls the deity's possessions simply put they were rendered to her servants