Well, it was a mirror, so it sure seems like you would just need to re-create the partition table and correctly sized partitions on the wiped disk, and the add it, then remove the left over entry.

This command would add a new device to the mirror

zpool add hgst mirror good_device_name new_device

And remove the old device

zpool remove hgst old_device_id

Or in a single step

zpool replace hgst old_device_id new_device

Links

P.S. Make sure that you have a good verified external backup, because you don't want to make things worse.