Un-hiding files permanently deleted from a synced document library

Hi All,

I have searched around a bit but I haven't been able to find a way to unhide files if a user deletes files from a synced document library that are "Available when online". 

When deleting the files the user get a message telling them that they will be permanently deleted from their own device. The trouble is users are users so in the case where this is done by mistake how do we get these files that are still in SharePoint to show on the users computer.

Thanks in advance for any suggestions.