Radial Menu is using a xml data file to store the menu information. The data file can be found in the following location: C:\Users\Username\Appdata\Roaming\Radial Menu. The name of the data file is rmenu_data.xml
In the same location you will also find a file with the name rmenu_data_bck.xml. This is a backup of the data file which is automatically made every time whenever Radial Menu is started succesfully. If for whatever reason the menu will start, you will get the option to load the backup file instead. Ofcourse it's good practice to backup the data file on another drive, usb stick, network location or other storage location.