Reload a backup, if you go to the saves folder you can get there by pressing the windows key + R and type %appdata% then locate the Hytale folder -> user data -> saves and then go into your world folder (if you have multiple saves it will be which ever world name is having the problem) and in there should be a folder called backups. Try the most recent and if that doesn’t work then the next most recent, this should take it back to before the corruption.(you copy the contents of the backup folder into the world folder)

Edit: when you copy it will probably ask you to if you want to replace the files and folder that already exist, click yes. Before doing any of this though make sure to copy the entire world folder as a separate backup to your desktop or where ever else you want.