In the current version there is no posibility for a user to recover a top level folder if he deleted it, but there is a posibility for the administrator to recover those folders.
If it is configured the folders are moved to BACKUP_REMOVE inside the storage base path of your server when a user deletes it. (Check Preferences → Storage → Move folders to backup directory when users delete them)
To recover those files just create a new folder in web interface for the user and move the files from BACKUP_REMOVE to the new folder in your storage. Make sure that the MetaData aren't copied to the folder too!
After the next scheduled scan of the folders the files are showing up in the web interface for the user.
Depending on the configuration of the server this takes either one hour or it is done at 0:00 in the night.
If the folder got encrypted it is not possible to recover the folder.