You could also just take an indirect route to get to DTW, for cheaper than nonstop, and not have to worry about getting caught/your ticket cancelled.

For example, MSP-ORD-DTW-ORD-MSP (which I just searched for, on two random business days in mid-January three days apart, and found for $300).

Use the "Multi-City" function on the delta website and play around. You probably can find some city where you A) can fly from MSP and B) that has a connection to DTW that has some good deals.