There's no way to retrieve a deleted mailing list, nor can we restore the list from our end. When a list is deleted, it is a permanent action, so delete with care!
Don't worry, it would be very difficult to delete a list by accident. When you click to delete a list, you'll see a confirmation window:
From here you can Cancel or confirm that you want to Delete. Once you click the green Delete button, your list is gone for good.