Board Thread:Warhammer 40k General Discussion/@comment-37.152.33.225-20131111163502/@comment-24114582-20131111175354

If a Primarch would return, there'd probably be civil war first, awesome conquering the galaxy later. I think that a Primarch would be a tad upset to discover that basicly all of humanity is now worshipping the Emperor, and if they disagree with that view, the Imperium will start some holy crusade against them, arguing that they are heretics and the like.

If they dont start a civil war, break a beliefsystem or just give up on the Imperium (which I think is actually the most likely scenario), there will indeed be an age of revival for humanity.