I know someone who was given a citation for OWI in March 2006; in June 2006, they sentenced him 60 days of local jail with work release and revoked his driver's license for 27 months.
He was then given a citation in May 2008 for operating after revocation(they included that the revocation was due to OWI); in October 2008, they sentenced him to a 6-month suspension on his driver's license.

So what happens if he gets stopped again? He's already got a hefty driving record, so would he get jail or is it just another large fine?

Jail time. He hasn't learned to not drive with a suspended license. Most judges don't keep handing out fines but get tough and give more jail time.

Depends on state, and at times judge, in most some jail time, but it could be just more suspension and a larger fine