Since private payments are stored only on your device(s), and updated every time you send or receive blackbytes, the best way to protect from device failure is to have a multisig wallet with redundancy, e.g. 1-of-2 is enough for backup.
How do I backup my wallet?
You can do a backup on windows and linux by copying the user's data folder. Look at the folders "c:\users\YOURUSERNAME\appdata for windows" and "~/.config" for linux.