Server broken after downloading 1.13

I recently got 1.13 on my server and wanted to put the finishing touches/play test a mini game I have spent over 14 hours on. The problem is there are chunks missing like random holes. Normally this wouldn't be such a big issue, however it targeted the command blocks and the walls that surround the map (huge with intricate detail). All of my hours of hard work is gone, unless there is a way to fix it? BTW I can go through these holes. I have an image but can't post it because it is not a link, it's a screenshot. So is there a way to get my hours of hard work back??

Solution 1:

Due to a bug, the game will have advised you to make a backup before opening the world in 1.13. If you have done that, you can restore it.

Otherwise, if you have no backup, those chunks are gone. They just got deleted. You can't even restore them using a file restoration program, because they got overwritten by the new ones (and aren't complete files themselves anyway).

Moral of the story: Always make backups! 1.13 was released in a horrible state sadly, so probably many people suffered a similar fate as yours.