ZPOOL replace defective disk in exported pool

I hate to say this, but do you know that you were basically adding unraided disks to your pool?
The command you provided basically says, "Add another disk to pool nas and stripe it with the existing disks."

Is that what you meant to do?

The pool is done at this point, especially if anything was written to the bad disk. If this were a pair of mirrors, the pool would be in state: FAULTED and you'd be able to recover. As-is, you've probably lost your data.

My suggestion to you would be to get a duplicate set of disks and ghost the raw contents over to the other set of disks for starters. Once you get the data restored if possible you then have the disks to make a mirror or other backup on. It will allow you much more leeway in trying to recover your pool that way. you are also leaving out important information like what mode you created the pool in. z-1 z-2

see http://www.joyent.com/blog/zfs-forensics-recovering-files-from-a-destroyed-zpool you may have some luck with that. I would also verify that the disk really is bad as well. If it isn't then you may have another issue going on like a flaky controller. if the disk is bad you may be able to deal with it by ghosting contents. I haven't messed with zfs importing disks enough to know if it is possible to tell zfs that the replacement disk is the failed one, especially since it is by id and not slot. It may not be possible to trick zfs in to using the ghosted data on a replacement drive to recover from the fault. That thought though is what comes to mind from my other experiances in computers.