In order for your downline space to be cancel, you would have to no-show an operating flight. When the flight is "closed out" at departure, that's when your remaning space would be cancelled as a no-show.

Since the flight you were scheduled to take from CMI did not operate, the flight close-out process wouldn't have happened and thus your itinerary would be left intact.

As for refund on the cancelled leg, it's certainly worth a try. However, I imagine you had a through fare from CMI - DTW. If so, the correct refund amount would be to deterine the fare ORD-DTW actually flown less the value of CMI-DTW you paid. It wouldn't surprise me if the ORD-DTW fare was actually higher than the CMI-DTW, in which case no refund would be due.