After a year, the Nether around spawn is a strip-mined wasteland and the End islands are picked clean. Resetting just those dimensions is the standard fix, and it leaves the overworld — where everything people care about is built — completely untouched.
What to do
- Announce it, with a date
Anything left in the Nether will be gone. People keep storage there, and portal-linked bases break when the terrain changes. Give them a week.
- Stop the server and take a full backup
Download it. This is a delete operation and there is no undo button.
- Delete the dimension folder
Remove
world_netherfor the Nether,world_the_endfor the End. On vanilla, removeworld/DIM-1orworld/DIM1instead. - Start the server
The dimension regenerates from the same seed the next time someone enters it. The terrain will be the same shape as before, but with all the resources restored.
Overworld portals map to Nether coordinates. When the Nether regenerates, a portal can come out inside solid rock or on the roof, and players end up somewhere unexpected. Warn people to break and rebuild their portal pairs afterwards.
Deleting world_the_end resets the dragon fight along with everything else. If your players want that, it is a feature; if they do not expect it, it is a surprise.
The overworld is unchanged and stepping through a portal generates fresh Nether terrain with intact ore and forests.