>>5507535There's no completely escaping that the Horus Heresy will be a shit sandwhich for everyone involved. No one expects betrayal like that on such a massive scale. Everyone was extremely bitter about how many trusted brothers turned traitor. Like you said, even Ferrus was betrayed by his best friend Fulgrim. TalOS isn't going to escape that some of those he worked with, trusted, even invested in will end up on the side that wants him dead.
I can only hope his paranoia at least lets him make contingency plans for everything, even the most unlikely. If a single space marine Thiel was able to seriously consider how Astarte v Astarte combat would go, even at the cost of censure, and the Iron Warriors are implied to have done simulated Legion vs Legion war simulations, it seems reasonable that TalOS could entertain the idea that however low the chances of a major civil war between Primarchs may be, it never reaches 0%, and have some plan for it locked deep away.
>>5507538Ahriman's a pretty major character for the Traitor side. Not impossible, but keeping him loyalist while not Magnus would be a very strange scenario. Still, it's a nice idea. The lodges were able to turn some of the loyalist traitors, and there were some loyalists among the traitors who didn't get slaughtered at Istvaan like Loken.
