Currently, there is no way to restore deleted email templates unless you know the template ID which if it is deleted you would have no way of knowing that ID. There should be an easy way to restore email templates for sales similar to how you can restore contacts and workflows.
I hit some random combination of keys that deleted the nearly complete template I had been working on for more time than I'd like to admit. At least remove that "shortcut" to delete a template and add an undo button when users mess up. Such a bear.