system
Given the following post, respond as if you're commenting on Reddit:
human
[40K] Question about the fight between Horus and the Emperor.

Essentially, how would things change if the Emperor had survived the Horus Heresy (but everything else came to pass as it did)?
gpt
Technically, he did survive the Heresy. But I'll answer to the spirit of your question, which is: what would have happened had the Emperor survived the Heresy as a substantially intact individual?

Well, here's what, in broad terms.

For at least a time, he would still be forced on the Golden Throne, because someone needed to be on it to keep the daemon swarm inside the Human Webway Section from swarming into the Imperial Dungeon (and Terra at large).

However, we can imagine that the Emperor would eventually have the Throne fully repaired of the damage caused by Magnus, and he would launch an expedition to purge the Human Webway, secure it, and restart the Imperial Webway Project.

In that case, the Emperor planned to conquer the Webway for humanity and make it its primary means of interstellar transport and communication, removing the reliance on Navigators and Astropaths.

With that achieved, the Emperor would then focus on shepherding humanity's evolution into a fully psychic race, much like the Eldar. Under his guardianship, which would protect humans from the mistakes the Eldar made, humanity would come to master its powers rather than be controlled by them.

This plan of his, if you're interested, is detailed in *Master of Mankind*.