Pretty interesting, there are now two DTW-ICN flights in the air, both operating as DL159.
DL159 (747-400) is in the lead:
https://flightaware.com/live/flight/...330Z/KDTW/RKSI
DL159 (A350-900) is chasing it:
https://flightaware.com/live/flight/...731Z/KDTW/RKSI
Sounds like the 747 will turn around quickly upon arrival to operate the last scheduled 747 TPAC flight. The A350 will stay in Korea overnight