He was briefly suspended after the DC-3 incident, but was back to flying status within 6 months of that. Dan eventually (a few years after the DC-3 arrest) upgraded to Captain on the DC-9 the last year that Delta flew the ex-Northwest -9s. He was offered to transition to MD-88 Captain, but chose to retire early at that point.
As to why he retired early, I can't say this is fact, but my suspicion is that he was in a good place financially and didn't really want to keep working full time as an MD-88 Captain. Dan loved his time as a wide-body FO living in base at ATL - he bragged about being able to stay in reserve status and flying one trip a month on the 777 leaving the rest of the month to play around with the DC-3 and other GA stuff. The short haul DC-9 and MD-88 schedules were a bit more demanding. In fairness to him, he went out on a high note - he really enjoyed flying the DC-9 being an dinosaur of a Douglas jet, it was right up his alley. With the MD-88, I think the juice just wasn't worth the squeeze.
Pretty sure Dan's oldest was off to college and the youngest in high school when he retired.