Fatal accuracy 

It is currently unknown, however, how he had managed to survive, as the Space Marine faction won the Kronus campaign (the fall of the Chaos stronghold ends with Eliphas' gruesome death at the hands of the vengeful Daemon Prince), or how he is now part of the Black Legion, as he was originally from the Word Bearers. However, accordingly to the 5th edition Codex: Chaos Space Marines, Chaos Space Marines of all origins are able to join the Black Legion. 

First of all I thought Chaos Space Marines were basicly immortal, when their body is destroyed aren't they supposed to return to the warp and to return to life? Secondly and as far as I know there's no 5th edition codex for the Chaos Space Marines but a 4th edition one.