As you said above: "The unexpired I-94 may protect him from accruing days towards 3/10 year bar though", that is because the person is lawfully present (or say "authorized presence") during the I-94 duration (unexpired) and thus, he is not subjected to 3-year or 10-year bar.
Lawful presence or unlawful presence is different from In-status or out of status. They are different concept though they are related, but not the same. When a perosn I-94 expires, his unlawyful presence begin to be counted until he leaves US or file I-485.
See this USCIS link:
http://www.uscis.gov/USCIS/Laws/Memoranda/Static_Files_Memoranda/2009/revision_redesign_AFM.PDF
