In the end, Humanity had actually managed to kill Celestia with a point blank nuclear detonation. The good news is that the barrier was erased and Equestria is in chaos, the bad news is that this only poisoned the rest of the Earth as all that magical radiation was free to spread across the atmosphere and Humanity's abuse of the planet means technological civilization as we know it can't be sustained. So either the last few Humans die out or abandon Earth alltoghether, your pick. Meanwhile, Pony civilization collapses as they struggle to support billions of new foals without any celestial guidance. So for the next few thousand years Earth enters a new dark ages as ponies all over struggle to pick up the pieces, but eventually peace and stability returns unshackled by a solar empress. Wars are fought on occasion but with the use of magic they manage to compensate for the resource scarcity of Earth long enough to make it to space. Thoughts?

Why would Celestia be hostile? Why use a miniature sun to kill her? How would that erase the spot where the magical spread hadn't reached yet? Can't they just immigrate to Equestria Girls Earth?

7280272
Conversion bureau cliches, the fact that the radiation in the atmosphere spreads, and Eqg doesn't really exist in these kind of stories :v

7280346
I thought the premise was "Earth and Equus' universes crash into each other, overlapping, but magic continues to leak out of Equestria and is SPREADING and is deadly to these kinda humans, and the only viable solution ends up being to become a creature from Equus whom the magic is harmless, and the social and political ripple effects that would inevitably result from this."

So all humans are converted?

7280393
Eh. I just wanted to focus on the rebuilding aspect
7280420
Yeah or in space. At least Celestia is gone

7279939
Their culture is gonna be whack af, but I would be interested in seeing where such a story would go!

7283519
Also depends on what your view on newfoals are. If they're mindless zombies then the normal ponies will use them as slaves and cannon fodder, if they maintain a degree of their previous lives, then the ones who were forced to do it out of self preservation would rebuild their old countries but maybe with Equestrian characteristics