Sudden crash + whole save file is gone

[Barni6264]

What happened?

1. Game started lagging (I was almost out of memory)
2. I got massive lag spike
3. Both the game and the downloader closed (ig. because I ran out of memory)

When I restarted the program, the whole map (all saved chunks in all dimension) were gone.
The files seemed to still be there though (maybe one of them is corrupted).

Is there an easy way to fix the world file, or should I read the the source and figure it out myself?