OP, if you don't mind, I have a couple of questions to better understand your process:

1. How long before the CMI-ORD flight did the cancellation become known to you?

2. Presuming you were unable to check in online due to the cancellation, how did you check in at ORD? With a human or machine? I presume human.

3. If with a human, did they note anything regarding CMI-ORD or merely check you in for your flight?

Based on experience, IMO you were lucky, regarding being able to bypass the cancelled segment and fly the rest of the itinerary. The refunds department should be able to access the fare construction and provide a partial refund. It may not amount to much but at least can partially offset your costs to get to ORD.