Great news, I was afraid you did not notify CIC when you landed (or before), that would have made you ineligible to sponsor your spouse.
So to answer your initial question regarding the status after the OWP expires. As your spouse currently has an OWP and that your spouse will apply for an extension of the OWP, your spouse should be on implied status between the expiration of the current OWP and the time CIC reach a decision on the extension. The very important thing is to apply for the sponsorship and the OWP extension before the current OWP expires.
On implied status, your spouse is allowed to continue working, however some employers will refuse to keep the employee until they show a new valid work permit. If that's the case, I suggest bringing proofs you applied for the extension prior to expiration and you can show this link to the employer:
http://www.cic.gc.ca/english/helpcentre/answer.asp?qnum=188&top=17