Ynnead

Ynnead is the emperor's soul which is held within the warp, Ynnead presence grows as the god-emperor of mankind weakens and he will be born once the emperor of mankind is reduced to dust, then and only then will the eldar fully understand that the new god of both mankind and the eldar will begin the soul link and help the emperor find his way out of the warp.

Ynnead will come out of the warp near holy terra and as soon as the imperium makes contact with the emperor, librarians will then discover that this is not a hostile threat from the eldar it is the emperor's soul within a newly fromed body.

a few days after then he will call upon the eldar faseer's to bring a mass amount of army, because they are going to wage war upon slaanesh and the rest of the chaos gods inside the eye of terror, the new empire will crush slaanesh and therfore restoring the power lost from the fall of the eldar.

after the after destorying the chaos gods all will be restored and the new empire will grow to expand outside of the galaxy.............