Is it possible to set up xenForo so that any deleted threads or topics move into a 'Deleted Threads & Topics' forum for review before being permanently deleted by Admin (Myself)?
Perhaps you could just get your staff to move the threads to such a forum. Change the permissions such that only select people can view that forum and its threads. Then just delete them permanently after they have been reviewed.
There are several addons that do what you want. I don't know if they're all still supported but they allow mods to send threads to a "trash" forum rather than deleting them.