ZFS dataset restoring
Depending on how long was you pool kept online after the mistake and also how busy was the pool during this period, it might be possible to rollback it to a previous transaction group (i.e. use an older uberblock) where the file system was still present.
Here is a script that takes that approach:
http://www.solarisinternals.com/wiki/index.php/ZFS_forensics_scrollback_script
You should work on a copy of your disk(s) as the recovery attempt is destructive.