This is the account of things from The Horus Heresy: Collected Visions.
In the aftermath of the confrontation between the Emperor and Horus, Dorn and the Custodes find the Emperor and quickly realise that he's just barely clinging to life. Dorns asks what orders he has and the Emperor weakly commands them to take him to the Golden Throne. They teleport there, meet the Khan and then rush to the throne where Malcador is near-dead. The tech-priests disengage Malcador and place the Emperor on the throne instead.
These are the final moments and words:
"At the instant of Malcador's death the Emperor awakened, as if somehow he had been boosted with a powerful salve or medicine.
The Emperor, still frail and weak, spoke, 'Poor, brave Malcador the Hero. He reserved a fragment of his strength for me. It gives me a little time to pass final orders to you all. If you do as I ask then I shall not wholly die, my spirit at least will survive. My injuries are severe, more so than I had hoped but less so than I had feared. My psychic powers will return to me in time but my body will never heal. I shall never walk amongst you again. I am now bound to this machine for all time. My faithful bodyguard and attendants know what is required. You must do as they request!
'Dorn and Jaghatai, you have much work to do. Though the head of the serpent has been destroyed its coils still choke the safety of mankind. You and your loyal brothers must fight on. Cleanse the taint of treachery from our stars. Never again must we allow the Ruinous Powers of Chaos to have such a chance. 'Now all of you go! You know your duties. Execute them well. The universe has many horrors yet to throw at us. This is not the end of our struggle. This is just the beginning of our crusade to save Humanity Be faithful! Be strong! Be vigilant.'
The Emperor spoke no more.
And that's that. I don't know whether things will happen similarly in the upcoming Horus Heresy novel. The language of it all might change since the speeches and dialogue in Collected Visions have quite a mythical and dramatic feel to them, like a grand performance or retelling.