Not heard that before. As soon as they're matured they can be removed without detriment as far as I know.
The OP is referring to the second progenoid, so the SM would actually have no progenoid left.
In the Gildar Rift
, the Silver Skulls actually discuss what they're going to do with one of their own, which this happens to. I haven't come across another similar situation, but I haven't read all of Black Library (yet
The slaves are how a Chapter is created in the first place, thousands of humans are implanted with geneseed and the various organs are harvested ready to be surgically implanted in aspirants in a newly founded Chapter.
Not disputing that, but the OP is asking about an existing Chapter, not a new one.
Considering the ritual and tradition that has built up around the implantation process in every Chapter I've read about, I can't see (not saying it isn't possible) a Chapter implanting slaves when they can just implant initiates/novitiates and begin rebuilding immediately.
Speaking of those slaves.... how do the numbers work out? I mean, I read it takes over half a century(i saw 55 years) to create those 1,000.
This is usually the number of years cited. Which is why I think it would make more sense for an understrength Chapter to recruit and implant initiates to rebuild their scout and reserve companies as soon as possible. Since even being understrength is no excuse not to go out on missions.
Given that progenoids absorb the genes from other organs, are all organs implanted? I guess then they don't follow the strict protocols regarding implantation?
I don't believe all organs are implanted since that would make the slave (I'm assuming implantation in slaves is what you are referring to) as close to a space marine recruit as makes no difference.
I haven't come across any story where the AdMech are creating a new Chapter, which I assume would detail the process.