I mistakenly deleted forever "All Mail" when trying to delete spam. My trash can had already been emptied. Now all the folders along the sidebar are empty. They contained special emails from friends and family. Guess I have to get over it.
If Gmail has not deleted the messages from the server, you can recover deleted emails after deleting them from your trash folder. You must open your gmail then click the drop down grey arrow on the left from your search box at the top of the screen. It will then ask you several question such as to: or from, subject, key words or date within. Click on the blue search button on the bottom left of the search box and all of your deleted emails will be revealed.