The world has died and is nothing more than ash and dust. The land of Equestria is a far off memory along with those who once inhabited it. Wandering the empty land is the sole survivor of the cataclysm that brought about the death of the world. Yet this sole survivor is also the harbinger of the world's death. In the final moments of the last living thing in the world, the story of how the world died is told. One of many ways the story could be told and one of many ways it could end. This is the day the sun set for the last time.
Season 5 Wasteland Timeline; No spoilers