I think bit-rot is as much (and possibly more) a problem than total data loss.
Bit-rot is an under appreciated problem, which is why I spoke of the importance of tested your backups and hinted at the fact that I had seen a bad case of bit-rot in production caused by a dodgy RAID card which the rotten files were then propagated onto the backups. Not a pretty sight and not one I would wish to see again.
ZFS can be cool if you do it right.
But its not a form of backup. Just like RAID is not a form of backup.