Add to this chaos the reawakening of the Void Dragon, the inevitable bid for power by Chaos and another Tyranid invasion.
The Void Dragon has a different role in all of this.
Trust me. The Emperor knows all about the C'Tan on Mars...
I won't say more, except this: Read Mechanicum by Graham McNiell. Best Heresy novel so far, IMO, and it sheds so much light on this subject...
Not much of a fan of the ranting in that story. Maidens? Mars? The kind of power ascribed to the Emperor in that begs the question, how could he possibly have even NEEDED the primarchs? Why didn't he do the same to the galaxy in general? The power he is given in that story makes the entire crusade and his painfully slow rise to power all the more ridiculous.
What I think would be more interesting is if the Emperor Gambit of the old shamans simply failed. They didn't create him for the purposes he set himself, he didn't even KNOW about the greater galaxy at the time of his creation. The shamans were very narrow in their reasons for creating him.
Thus, just because the souls of some Australopithicus africanus reincarnated into a single form DOESN'T mean that he is galactically destined to actually DO anything. There is every chance he isn't strong enough or even capable of doing what they wanted him to.
There is no reason that other psychic races couldn't create their own 'Emperor', the process as described is not a unique thing, the Infinity Circuit of the Eldar is very similar to the Emperor, just not as focused.
So I would like to see something OTHER than 'teh empra roxxors'. He doesn't roxxor, he's failed his stated objective and he wasn't created by infallible beings so isn't destined to fix everything. That's what he WANTS to do, but wanting and destiny are seperate things.
I would think something more interesting would happen. For instance, the Nicassar create an Emperor gestalt, or several mini emperors. Ynnead forms etc.
I'm over the Emperor being the centre of all things, considering that from an objective perspective he never was nor will ever be. That's an arrogant conceit on the parts of his creators.