And, if you do manage to find the disk and get it to reimport, the first thing you should do is a backup.
Once you've readjusted the other admin (with the clue-by-four), may I suggest reading some of the excellent how-to guides here on the forum, to better understand how things work in ZFS land? Some of the usual assumptions you make with your average boring RAID array are out the window where ZFS is concerned. I've dealt with some decent size NAS and SAN arrays in my day... getting started with FreeNAS was still a bit of a learning curve.
Once you've readjusted the other admin (with the clue-by-four), may I suggest reading some of the excellent how-to guides here on the forum, to better understand how things work in ZFS land? Some of the usual assumptions you make with your average boring RAID array are out the window where ZFS is concerned. I've dealt with some decent size NAS and SAN arrays in my day... getting started with FreeNAS was still a bit of a learning curve.