http://redlib.r4focoma7gu2zdwwcjjad47ysxt634lg73sxmdbkdozanwqslho5ohyd.onion/r/books
When they die they go into "the vats", some sort of organic matter recycling system which produces their food and various other substances which, again, are left to the imagination. They use "breeding stumps" kept alive through ghastly machinery to reproduce en masse. When they arrive in the book it feels like you are reading a particularly well-done piece of Warhammer 40k writing.