At the end of the campaign, after the defeat of the forces of Chaos, we still don't know what became the Deceiver and who was instructed by Abaddon to kill him.
We can read it on the Final Report :
So... which Chaos Lord Commander of the Black Legion killed Ygethmor?With scant hours to spare, the Chaos Space Marines, and those other servants of Chaos who had the means, fled the planet and left utter devastation in their wake. A whole world lay blood-soaked and burning, torn apart by their brutal ministrations. Only Ygethmor, his coterie of bodyguards and acolytes, and those mutants and traitors unworthy of salvation, were left behind. The commanders of the Black Companies sent by Abaddon had very specific orders concerning the fate of Ygethmor: he was to be given every assistance, but if he failed, they were not to bring the sorcerer back with them.