Although it is entriely possible that CO will dimish or even abandon its hub at CLE, the cirmcumstances that might lead it to do so are pretty different from what happened at PIT.

At PIT, the airport authority built a very large, very expensive new airport terminal at the behest of US. But when the authority wanted to pass the cost along to carriers, including US, in the form of landing fees, US made the decision that its interests were best served by concentrating its East Coast operations at PHL and CLT.

A big part of the calculus, then, was the high landing fees, although it is certainly possible that US would have exited PIT even with lower landing fees.

At CLE, landing fees are average, there is no new, monumental terminal. With ORD, UA's primary hub, only slightly over 300 miles away, it is certainly possible that CO would abandon this stretch of territory, turn CLE into a secondary destination, somewhat akin to the treatment STL received after TW was absorbed by AA, and allow UA and ORD to provide the bulk of the northern mid-central hub traffic (IAH would be the southern mid-central hub).

Perhaps there is still room for a CO hub at CLE, though, even with a tight integration with UA.

And one of the factors playing in CLE's favor is its reasonable landing fees.