It looks like the replacement flight # was supposed to be DL9842, but then it was canceled:
From EF:
FLT INFO 512/28JUN ***
STUBBED TO 9842 ***
LOF ARR DEP ETA ON IN ETD OUT OFF ACF
MEX 220P 644P 657P 720P 319
DTW 744P 1214A 1202A 1209A
FLT INFO 9842
DTW 1005P LX LX LX M88
MSP 1058P LX LX LX
FACTS-
MEALS/CPT C Y
MEXDTW L F
DTWMSP CXLD
FlightView shows a DL9937 MD88 flight that was supposed to leave at 11:45 PM DTW/MSP, but I can't find any other info about it.
Hopefully the OP will come back and fill us in as to the details of what ever happened to him or her!