If his temporary permit expires in the meantime and he can't extend it, then he can apply to change his status to visitor while he waits.
I'm also a temporary worker and my PR application, together with the OWP app, is already in process. My temporary work permit will expire in January so I phoned CIC and they told me that I can still work for the SAME employer even after my TWP expires since I already submitted my application for an OWP. No need to apply for an extension or change status to visitor while waiting. As long as the OWP app is already submitted and it's the SAME employer and not a new/different one, there won't be a problem. "Implied Status" was what she called it.