Okay, this story is officially done! If I continue, I think I will start telling the story of Luminous, the pwi-Necrons stationed there and possibly some smaller sections showing what's happening elsewhere. Possibly some things Manric is up to, serving under Zahndrekh. But since this is 30 chapters, I think I should break it up so keep an eye out for the next story!
Now for a bit of trivia. Not necessarily 40K canon, of course, but just the canon of this "universe".
The drukhari looted the ancient spear from a museum when they were escaping from Slaanesh after the destruction of their empire. Since they couldn't get it to do anything out of the ordinary, they decided it was probably a replica. It did occur to them that the spear just hated them, but they shrugged a bit and used it to shed more blood. The spear was glad to get away.
It would require some deep research and possibly help from the aeldari in the spear, but creating a soul stone that can house a soul, then returning it to a biotransferred human, should be possible. Also creating entirely new souls for the Necrons is technically possible but probably an awful idea since the ones that could most easily do it are the Ruinous Powers, particularly Tzeetch. You probably don't want a soul made by them.
Yantek comes from a very large rural serf family. He had six brothers and sisters as well as numerous cousins and nieces and nephews. We might see more of his relatives in the future.
The four planets they are being tasked to garrison are two Civilised worlds, a Feral world and a Hive world. The Hive world in particular is going to be pretty offensive to the Hope humans and they might request permission from Imotekh to clean it up, particularly if Hope's technological advancement is on track. Hive Worlds violate the Code of Terra on an hourly basis.
The Code of Terra is a pretty simple code that dictates what cannot be done to humans, and what basic rights they have. It's meant to be the bare minimum that any culture should follow, so it does not address many, many things. For instance, humans do not have a right to food or shelter, as those things must be earned and a colony often cannot support dead weight. However, humans have the right not to be forcibly lobotomized and implanted with cybernetics. Also, humans have the right to not be exposed to extremely toxic chemicals, and the right to a certain amount of sleep if they are expected to labor. Things like that. As you can imagine, servitors will give Hope humans the same feeling of HERESY! That pwi-Necrons give the Imperium. But they will be nicer about it.
The Code of Terra does make an allowance that slaves are not subject to most of the provisions of the Code of Terra. However, the status of slavery can only be granted to those who have committed crimes that are worthy of a death sentence. It is also noted that tightening the criminal codes to create slaves violates other Codes on the right to a fair trial.
Because the Code of Terra is considered so basic, violations of it are a very serious matter and the STC in particular takes it extremely seriously. In the ancient Terran confederacy, repeated and serious violations of the Code of Terra would make a planet a Pariah World that would not be visited or assisted in any way. Because of that, the STC will consider all of the Imperium to be Pariah and even if it were captured, it would refuse to help them in any way. It is even possible that the STC would no longer consider Imperial citizens to be human, although it could probably be talked out of that particularly harsh stance.
Hope is an extremely patrilineal world where women are fundamentally expected to become mothers. This is largely due to the intense population pressure the drukhari could exert on the planet, and because of how long it went on for, this won't change anytime soon. In addition, Hope actually desperately needs to expand the population and then start colonizing other worlds. So women will be expected to be mothers and have as many children as possible for a long, long time.
While the God's Hands won't go out of their way to proselytize, they also won't be shy about telling anyone who asks about their religion. It's possible their particular brand of Christianity could make a resurgence. Also, their particular branch of the faith does trace back to Catholicism but is essentially a schism that has many, many differences and then has drifted off for five thousand years. More really, since it was already pretty different before they left Terra.
While Trazyn won't dare offend Imotekh by taking Manric and his spear, if Manric ever has a very fatal and messy demise that doesn't allow for recall, that spear will be in Trazyn's hands faster than you can say boo. The spear won't be too thrilled about this, but what can you do.