Well, the good news is your music is intact. The bad news is there is no way to "restore" your library from an export device. If you had a main (internal) library copied somewhere, you would be in good shape.
As of rekordbox 3.2, you're able to actually store your library AND the database on the same drive, so if you're like me and keep your music on an external drive, you can store the database on the same drive and move it from computer to computer. Of course, it's still advised that you keep a backup of everything, but it makes it simple to maintain your music library if your computer's hard drive crashes.
In order to resurrect your music, you'll need to first install rekordbox on your computer (it can be the newest version; you won't have any info from your old library available), then bring all the recovered music into the library. It's a bit like starting from scratch.