CO did cut service to a lot of cities: FNT, MBS, AZO, SBN, FWA, TOL, ERI, CAK, AVP are the ones that come to mind. Someone mentioned DAY, but COEX still flies CLE-DAY. Part if it was due to congestion, but part due to economics.
CAK, for example, was definitely due to congestion: the planes out of CAK were often on long ATC holds because CAK is literally within the approach pattern of CLE, and often, they couldn't find a slot for the planes out of CAK. I don't think CLE-CAK will resurface, although I think COEX should consider CAK-EWR, which would be a great route for possibly twice-daily service.
I think TOL, ERI, FNT, MBS, FWA, etc, were cut in part to congestion, but in part to the feeling that a profit couldn't be made with RJ's in those markets. I have heard that TOL, FNT, FWA, AZO, LAN and SBN may re-acquire COEX service as early as next year, but no definite word on that. CO/COEX still would like to expand once the dual runways are up late this year, but, at least in the short-term, with the airline industry struggling, and CLE's landing fees still so high, I don't think it'll be a major expansion at this juncture.
And, while I'd hate to see the Beech's back in CLE, it might be the only way to offer service to cities like TOL, FWA, SBN, LAN, etc. I just don't think and RJ CLE-TOL would bee too profitable.