I’m not sure if most people are aware but if you empty your deleted items or accidentally delete a public folder you can restore it by clicking on its parent folder and going to tools>recover deleted items.
However, occasionally when trying to restore a public folder you may receive an error:
Outlook was unable to recover some or all of the items in this folder. Make sure you have the required permissions to recover items in this folder, and try again. If the problem persists, contact your administrator.
You can still recover these items by downloading a utility called PFDAVAdmin. I’m also under the impression you can do this from within OWA but I’ve never tried it before.
The PFDAVAdmin utility is pretty straightforward. You put in the address of your Exchange server and your global catalog server. Once you do this you should be able to view all of your public folders right click on the parent one and recovery the deleted items.