The Emperor was psychically corrupted at one point?
Man I barely know anything deep about WH lore.
When I say 'corrupted' I don't mean like 'external mind control got into his brain and changed him into a gross tentacle monster,' the way we usually use the word 'corruption' when discussing 40k.
I mean in the more traditional sense of 'absolute power corrupts absolutely.' I gather he was a relatively nice guy back in, like, 20000 or 25000 AD, but that he to some extent was warped (small-w warp, not capital-W Warp) into the domineering, callous jerk we know and loathe
after his decision to pursue a path of galactic conquest.
On another topic, the Emperor popping up is probably inevitable, since Humanity has already been shattered since the age of strife began in M25. The fall of the eldar happened in M29. He's going to do his thing no matter what happens with the Eldar, in all likelihood.
Maybe. But there's shattering and there's shattering, and presumably the point where Adam/Revelation decided to become the Emperor happened some time
during the Age of Strife.
The Emperor isn't psychically corrupted, he's psychically fractured. When he got put on the Golden Throne, he basically just became a very powerful psychic battery. In the process, he lost his humanity and other bits and pieces of his personality. One upside to the whole process however is that while he is physically crippled, his psychic power has grown immensely, to the point of rivaling the Chaos Gods. That's likely due to the worship he's getting from the ENTIRE Imperium. I don't think elaborating further makes any sense, since it's a bit off topic.
Well, part of what I mean is that even before that, he was a callous asshole to the Primarchs. A lot of the mistakes he made in life
before being put on the Golden Throne are directly attributable to him being kind of a bad person and deeply fixated on grand ambitions, big megaprojects, and sweeping conquest to the point where he couldn't really even interact with other people as people, or see the Primarchs as sons in any meaningful sense of the word 'son.'
If there is no birth explosion, then the warp storms might linger around which is obviously be bad for everyone including us, unless we do something like create our own webway.
But would make it so the great crusade doesn't happen, or at least doesn't happen until the galaxy calms down.
I'm pretty sure that if Slaanesh is never born, the warp storms that were gathering because Slaanesh was
about to be born... well, they may not just all go 'poof' all at once, but I suspect they'll wander off muttering about cosmic blue balls.