A shunt fed grounded tower could work well if the physical height is at least a quarter wave length and the ground radials are still intact. Another advantage of grounded towers is the lack of RF isolation modules on the other services and no no Austin ring transformers for tower lighting. Of course the nighttime power (if there is any) will have to be refigured.Cell towers don't tend to conduct AM signals very well, and AM signals only have so many places they can move.
One should assume Cumulus signed long term transferable leases (50 + years) when they sold the properties. There also should have been "business disruption" clauses too.
If any AM station has positive cash flow, I seriously doubt it will be signed off unless there is tremendous value for the land. Since Cumulus doesn't own the land, there is no reason for them to give up a station unless the landlord makes it "financially" worth it to them to give up the lease.