He watched. He always watched. He had little else to do, while He waited for His body to finally succumb to entropy and die. The life-supporting technologies of His golden sarcophagus were exceptionally good, even by the standards of the old Imperium in its technological heyday, but they were still imperfect. They would not sustain Him forever, in spite of the monumental cost willingly paid by the citizens of the Imperium; the thousands of souls sacrificed to the Golden Throne every day. It filled Him with sorrow, but He could only justify it by reflecting that without the thousands willingly given, the Imperium would collapse and trillions would die.
He watched His subjects go about their myriad lives, and felt a mixture of righteous pride and disgust at what the mighty Imperium had become. The one thing He had tried to avoid was the Imperium of Man descending into a totalitarian theocracy. Humanity was meant to accept logic and science, not fear and superstition. The Ecclesiarchy dominated, able to cow even the High Lords of Terra with the threat of an accusation of heresy. The Inquisiton would, of course, be quick to persecute the victim of such a claim. He only wished they could focus their zeal on the persecution of His Realm's true enemies.
Despite being immortal, despite the awesome psychic power He still yet wielded, He was not a god. It galled him to know His name was being used as such, while He was unable to speak out and show His subjects the better path. Were it not for the duty and love He felt for humanity, He would have given in long ago to despair. But that could not happen. He would never submit to the Ruinous Powers, those self-proclaimed Gods of Chaos. He would not let them feed on His soul.
His body was broken, and His mind splintered. He was literally a shadow of His former self, unable to move or verbally communicate, and His marvellous mind slowly succumbing to the warp. The greater part of His mind was dedicated to shaping the song of the Astronomican, guiding the fleets of the Imperium as safely as possible through the terrors of the Immaterium. He saw it, the currents of raw emotion, the winds of sentience, the colours of life. He sensed the Chaotic malignance, held at bay by the strength of will behind His psychic shout, the beacon that anchored the Imperium. As the main fragments of His mind and soul were permanently residing in the warp, it seemed only a matter of time until they dragged the rest with them.
Smaller parts of His mind wandered the Imperium at will, influencing the most important battles and crusades, causing even more superstition and giving the Ecclesiarchy even more power over the Imperial citizenry as they declared soldiers and warriors touched by these influences 'saints,' and beaitified the lot of them. It only made Him reluctant to lend His hand more often, for fear of making the theological situation even worse. But, His mind in its fractured state, He was unable to divine a way of correcting the error.
The rest of His mind was left to stagnate in his carcass, surrounded by the Companions of the Adeptus Custodes, to ponder His inevitable end and the stagnation of the Imperium.