You can try this:

- start game, click on the 'show player log' button thats on the bottom left.
- this will open a folder where all your stuff is saved and stored.
- go to the worlds folder.
- IF your worlds name is there, but has only files with the .old extension you can try renaming the files to delete the .old extension (make sure to first copy the files and put them somewhere safe so you can restore the folder if you need to)

This should allow you to open the world at a previous state.
This trick can be used to recover characters as well.

You should also back up the whole folder from time to time to ensure a bug wont wipe out your game.

Hope this helps.