Quote Originally Posted by Gwhizz84 View Post
Luther is definitely still around, it's the D.angels greatest secret. I don't think it's been stated what happens to his gene seed, probably something in the future I dunno.
Luther was never made into a full-Astartes, similar to Kor Phaeron. He was physically enhanced and given other implants, but he was not raised to the status for a full Astartes battle brother due to the fact that he was too old when the Emperor arrived upon Caliban. As such, he actually has no gene-seed inside of him.