Delta seems to be cutting the PDX-ATL red-eyes on certain off-peak days later on this fall, so unfortunately it sounds like you've fallen victim to that schedule "optimization." The DTW service is typically seasonal and the schedule now reflects that service ending on October 31, so your second change makes you victim of one of DL's favorite games lately - listing seasonal service as year-round until they get around to deleting the off-season flights.

As for your problem, the only option for remaining on a red-eye would be to leave earlier in the evening from PDX on AS/QX and connect through a larger DL station on the west coast. DL doesn't codeshare on PDX-SEA service (which shouldn't stop you from getting them to re-route you there if desired), but you can get DL codes on PDX-SFO/SJC/SMF/LAS/PHX/ONT/LAX. Depending on the time you're able to leave PDX, there are red-eyes to ATL from all those cities, not to mention DTW and MSP.

If you want the shortest possible detour out of PDX, I would recommend QX 2056 or QX 2174 on PDX-SEA, then connecting to the appropriate MSP, DTW, ATL, or JFK red-eye that would allow you to connect to your final destination. However, if you want to take advantage of their schedule change to maximize mileage, you could specifically request to route through LAX - just be sure your connection allows time for that.