Not sure I follow? The update process does take a backup, and places it in the same folder as the real database. As it is not possible to proceed with the new database, it is loss-free to simply recover the backup database. If we fix it to give it a better name, it should even be simple to figure out which file to restore.
If you have an existing database (the one for the backup, not the server) and run any operation on it using 2.0.3.13 it will be messed up. So all backups that you have attempted to run with 2.0.3.13 are likely broken. However, as mentioned above and in the other release post it is possible to recover simply by copying in the pre-upgrade database backup.
And much appreciated! If no-one tried the canary, we would hit all the unsuspecting users running the beta releases!