system
Given the following post, respond as if you're commenting on Reddit:
human
[Warhammer 40K] The Emperor is brought back to the pinnacle of his strength and majesty right now in the current Lore, what changes? Also a bonus question about the surviving Traitor Primarchs.

Cadia has fallen.  Roboute has been back for over a century.  The battle on the Moon has taken place.  The Plague Wars were a victory for the Imperium.  The Emperor regains full life, vigour, power, and majesty.  What changes now?

BONUS question: could the reborn, full power Emperor turn any of the Traitor Primarchs from Chaos to his side if he and any individual surviving Traitor Primarch were just teleported to a room together?  Would the sight of the full powered, reborn, glorious Emperor have such an impact on any one of them?
gpt
Well for one the people who should be afraid of the Emperor the most are his subjects. He went to great lengths in the GC to destroy religion and any spiritual beliefs and there’s no reason he’d stop now, infact he might be willing to “start from scratch” in the sense that he’ll rebuild the conquest and humble every planet once more. Keep in mind this guy ran a galactic genocide campaign.

Think about it like this when playing CK2 as Byzantine, you are rendered incapable and all of a sudden your regent/chancellor decides to hand over all your domains to himself and lower crown authority to a minimum, all the while selling off your genius/strong trait daughters to some nobody nomad. The first thing you do when you are forced to play as weak, hunchback, slow, drunk heir is dedicate all your energy to his destruction.

And about the traitor primarchs, they are beyond saving since there was a reason he specifically destroyed Horus’s soul, so that he may never be revived again since he already belonged to chaos but did not give his soul to them.