How do you Know if your Minecraft World is Corrupted?

Fix Corrupted Minecraft Worlds: A Simple Guide

If you cannot see your world in Minecraft, navigate to the worlds folder and see if the file is still present. If the file is there, then it could be that it is corrupted and therefore the game no longer recognises it as a valid world.

What do I do if my Minecraft World is Corrupted?

From your Home Screen, go to Settings > Application Saved Data Management.
Select Saved Data on USB Storage Device.
Choose Copy to System Storage.
Select Minecraft.
This should restore your world back to its former glory, providing it's available, of course.

What do I do if my Minecraft World is Corrupted Bedrock?

Uninstall game.
Clear local saved game data (System->Storage->Clear local saved games)
Clear MAC address (network->Network settings->Advanced Settings->Alternate MAC Address->Clear.
Reinstall game.
Attempt to load game.