Provided you haven't opened / closed rekordbox more than 3 times, you could possibly pull it from a backup. Open the following folder:
Win 7/8/10: C:\Users\yourusername\AppData\Roaming\Pioneer\rekordbox
Rename datafile.edb to datafile.edb.old
Rename one of the datafile.backup.edb files to datafile.edb (removing .backup)
Restart rekordbox and see if the playlists you had deleted are still there.