The submit to SharePoint can be added to a button whether it is a submit button or via a rule on another button. It is an action of a rule.
Saving to a file share or any where else is a submit data connection as well.
You can go into form options and remove the ability to save the form manually by your users. Once the form is in SharePoint, if the users have the authority to move files around than there is not much you can do about that in InfoPath.
I often had a secondary submit that would store to another SharePoint library or file share and I raraly allow users to save forms themselves, I think it is much better to be a controlled and standardized process.