The Void Dragon would die.
His legacy and armies would disappear.
And be forgotten.
The mighty Necron would be hunted and utterly destroyed, their liquid silver armour turned to ash, every last Tomb-world would be virus bombed into the dust.
He continued, his stride never faltering until he came across the form of the Void Dragon, on a knee, trying desperately to regain his feet. With one mammoth hand he lifted the star-god up by his armoured collar and called all of the destructive power of the warp which he possibly could.
The star-gods powers held for but a few seconds, then they were both consumed by a great fire of warp energy. So powerful that the Chaos gods themselves sensed this and shied away, for it also came with a message for them. They weren't the masters of the warp anymore, he was.
The raw fire burned away the dragon's indestructible liquid armour, fluid burst forth and was just as quickly turned from liquid to gas, his wings just disappeared and the dragon turned from a creature of metal to one of metallic bones. Then with one last metallic scream that could be heard across the universe he vanished in a whiff of black mist.
The emperor saw the creature's soul, a humanoid being in rotting black robes, a pair of black leather wings stretching out in a width of twenty meters, through the darkness of its covered face it looked upon him with feral, hate filled eyes. Then the fires of the emperor's power fell upon him and his spirit was burned from the universe, his last great metallic scream a final testament to his existence as one of the great destroyers of civilisation.
The fires which the emperor released could be seen from space as a great lance of power which swept forth from the planet's surface and disappeared into the distance. And once it began to cease every surviving Necron vessel, from the small packs across the inner system to the vast armadas which assaulted the outer defences, all of them vanished into nothing. The last armies battling on the habitable worlds of the Sol system also vanished from sight. Entire valleys once full of the monstrous cyborgs became eerie and silent as they vanished like wraiths.
Tell me if that isn't awesome.