Hi Amanda,

Unfortunately deleting a course does actually remove the records from the database. If you have any moodle course backups of those courses you should be able to restore them, or alternatively if you server has any scheduled disk backups from before the time the category was deleted then you could restore them to a staging site, backup the course and restore in your live site.

If you don't have any backups I'm afraid there's not really anything you can do. 

Simon