The forms will not be deleted without user action and a confirmation dialog. Almost every time a user feels their form disappeared the issue is signing in with a different email (AdobeID).
Did you close FormsCentral and then sign in again? If you did please try signing in with any other possible emails you might have used and see if your form is simply in another account.
Just to confirm, this was a form that you authored (created from a Template) and not a form that someone shared with you, if the form was shared the author could have removed the share.