If the city wants out, I'm not sure how wise it would be for NASCAR to insist on the full three-year run. Chigaco would probably do the bare minimum required, since it wouldn't be interested in the success of the event. Disgruntled citizens and disappointed attendees may reachnegative opinions of the body. Potential host cities may wonder about getting the short end of the relationship stick.
Still, NYC and Boston don't mind roping off 23.2 miles every year. Miami and Vegas seem agreeable, but there's those pesky local tracks that will want to keep their existing dates.