whats the life expectancy of a NAS? if it dies, can I just plug the drives into a new one?
Others have said that the drives are the weak point here - the NAS itself should last quite a while. But to address your second question - "maybe" (assuming you meant "and keep the data on them"). It will depend a lot on how the RAID on the NAS works. If it's just a Linux md RAID then you could probably pop them into a new Linux system and get them to mount (there will be issues of "drive order" you will need to deal with). Again if it's using standard zfs or BTRFS raid-like filesystems you would be fine. If the NAS has its own RAID or hardware RAID then likely not.