As for psyker vs weapons(pyromancy vs flamethrower for eg), unless you are using orc weaponry, guns are much safer but an psyker never ran out of ammo.
As for Prosperites, now in the planet of sorcerers(Sortiarius), they suffer way more from mutations and the population of the planet is almost 100% composed by slaves, used for bizarre mutation experiments and hard manual labor and even if a slave manages to flee, he will probably become food of some bizarre mutant creature,
Talking about bizarre mutant creatures, can a syster of silence undo some mutation made using psyker powers?
And what type of planet we will gonna to see in this game set in koronus expanse?
And how the imperium deal with heresy with planets outside of the imperium by their ignorance? Eg - Lets suppose that the imperium finds an planet hwich uses "abominable intelligence", that tolerate the existence of mutants worships another deity which isn't the big E or anything like that? Will they go full "burn the heretic" or try to persuade them and if fail, go full exterminatus?
Other question. Since mutilations will be part of the game, mechanical limbs will be too?