Today let's take a look at how the Primarch Roboute Guilliman plans to destroy the Imperium of Man as we know it.
Since his return from death Roboute Guilliman, the Avenging Son, has been hard at work. On the face of it, Guilliman has spent every waking moment (which is his every moment since he no longer sleeps) working tirelessly to shore up his father's realm.1 He has rebuilt the Space Marines by introducing the Primaris, fought the Indomitus Crusade, and the Plague Wars, battled across countless stars, restored the glory of Ultramar of Old, and passed numerous reforms aimed at restoring the Imperial Government.
In a galaxy wracked by war, Guilliman has been everywhere, a shining beacon upholding Imperial might and bring hope to the teeming trillions of faithful. It can well be said that without Guilliman, the Imperium of Man would not have survived the cataclysmic events of the 13th Black Crusade and the aftermath. Guilliman has, through super (or post) human effort, saved the Imperium for now. However, it remains to be seen if the Imperium can survive against an even more significant threat: Roboute Guilliman.
Guilliman, the Imperium's Foe?