I don't think you have to maintain the status if you have already submitted the application via inland sponsorship, however, according to CIC website, you do have to write an explanation letter on why you fail to extend the visa before it expires.
Submitting the sponsorship doesn't give you any status. If you'd submitted an OWP, then you have maintained status, otherwise you do need to maintain your status in Canada as the sponsorship alone doesn't do anything.