What would happen to the world if all sentient species all disappear?

When Equestria is no more, can the survivors unite against foes once thought defeated, alongside two powerful new forces?

How would Equestria fare with an alien that commands a powerful army?

Princess Celestia has been gone for a week now, Equestria is in shambles. But what if a metalic creature crashed in front of Applejack's barn? I will need 100 likes to make a sequel or a prequel!