Minecraft: The Story is NOT done.

When you defeat the dragon, in final credits, the final words "Wake up" may be changed to "Wake up, your story is not done." Looks like a normal change, right? No! When you appear again, your world is dying slowly, there'll be giant holes that lead to the bedrock [not breaking it, obviously] and fallen trees, destroyed villages, lava everywhere. The Nether will be unaccesible. Day will never exist, and night is everywhere. Mobs spawn all time, some very strong. The only way to stop this is to go to that Stronghold you activated, and destroy the portal with a new pickaxe "The Eternity Pickaxe". It can be called any name, anyway is necessary to destroy the portal. World will restart, and everything is gonna be normal again.