This is an interesting question, but isn't the RAID/NAS under discussion supposed to host backup files? So, if your RAID fails, you still have you original data (on another HD, or on another PC, presumably)? And if your original PC fails, your RAID is still working?
It would be a really bad day if both systems failed simultaneously. That said, this approach is still vulnerable to theft, fire, flood, earthquake, electrical anomaly, etc.