This is benefit of the Thousand Sons legion. We don't have to replenish our numbers, we our always a 1000 and always the original. The Rubric Marines are just power armor and can be repaired if damaged. And in one of the Space Wolves books it mentions Thousand Sons are capable of resurrecting their Sorcerers if they die. It is ironic how little changes in the legion.
Now lets not argue about who killed who. But in all Chaos does have ways of finds new recruits to replenish the ranks.
I seem to recall reading somewhere that a Chapter could be recreated from a single geneseed (though it would take hundreds of years). With sufficient slaves, you could create geneseed farms, harvesting the geneseed from them to implant into worthy candidates. It expect it would be a slow and resource intensive process, but would probably work for some of the larger Chaos forces out there.
Yeah what i have read they get their warriors from new traitors but hey also have the same ways to create chaos spacemarines as the spacemarines has. And lets not forget that the most beloved of subjects never die whole but end up in some daemon realm of their chosen god.
I'm pretty sure that in the Word Bearers omnibus, the legion still collect's they're fallen's gene seed. They also harvest the gene seed of the loyalist SM's, as well as armor and other gear.
quite a few converts (loyalist marines turning traitor) but most are slaves and other humans in the local regiens that are given the same bio-engineering that loyalist marines get. Also remember that there are still A LOT of chaos marines that were alive in the horus heresy.
