Corennus wrote:There must be some marines who survived the heresy and were loyal from the traitor legions, but the vast majority died in the Virus Bombing and Dropsite Massacre.
I think most marines were rounded up after the heresy and tried. Don't think many were found innocent
I remember reading in one of the later
HH books that there were catacombs deep under Isstvan III, and that the emperor's children's Dreadnought had disappeared shortly before the orbital bombardment. There also may have been some hint that Saul survived too, but I'm not sure.
I can't fathom why they would make traitor legion loyalists into chapters though. The reason is because it could be inferred that their geneseed is part of the catalyst for the fall of the traitor legions. Many of the legions had quirks that were opposed to the emperor's edicts, like word bearers and faith, thousand sons and sorcery, and the world eaters and drug induced brutality. So why would they bring those "evil" traits back into their armies?