1. If you delete the form definition in Contact Form 7 or Fast Secure Contact Form (whichever you are using) that does not affect the data. The form data still appear in the Database section (assuming some data was posted).
2. In the Database page, you can click the “Delete All This Form’s Records” and the data is deleted and the form no longer appears in the Database page (but if the form is still around and someone posts, then it the form reappears on the database page with that new data).
3. On the database page, it doesn’t know if a form definition exists; it only knows if there is data in the DB for a form. So when you create a new form definition, you don’t see anything in the Database page until something is submitted form that form.