The BOLAdmin tool has a page that pops up if you hit this button instead of the delete user, i.e.
The Group Removal involves the following:
* Removal of the Workspace associated with the Group (if present)
* Removal of any access controls
* Removal of the group from the BeehiveOnline system
* Removal of the Group and members from the APEX group management system.
Once this is complete the group will be completely removed and the name available to be re-used
Do you wish to Continue?
and you have continued with the deletion despite the warning which clearly states the workspaces associated with the group will be deleted as well as the group.
Unfortunately, we are unable to restore individual workspace as that would require the restoration of the complete system and then the export/import of the Workspace so unfortunately you will have to recreate it.