Regardless of the state of the auto industry DTW is far too valuable of an airport to pull out of. The runway configuration allows for minimal to almost zero delays. In fact it's rare to even be delayed going to DTW. It usually only happens when the winds swing out of the west & the X-wind limitation for many airplanes begins to be exceeded. You can also reach Asia & Europe non stop. The global position of DTW is invaluable.

I can see MEM, CVG, or even MSP or SLC closing before DTW.