The trick is just to make sure that you have multiple backups on different physical storage devices. I have my iTunes collection backed up by having it on 2 iPods and a nightly backup to an external Hard Drive.
The chances of all 3 failing simultaneously are practically zero, so no matter what happens, I can always re-establish the original data and replace the failed device.
Of course to be totally foolproof you would need to have a backup in a seperate physical location, but it's not very practical for most