I fully understand your point, but I think having a very high quality manager mitigates the "issue" to some extent.
I guess they could have told Cora, "We will highly encourage the next GM to keep you as our manager, but no guarantees. If the next GM wants to fire you, we will make a space for you in upper management with a hefty raise. Is that okay with you?"
I doubt, he'd say no, but he might have.
I'm not saying the situation is not dicey. I'm just saying I think Cora is good enough to want to keep around.
They may value him more than the next GM, and maybe they are not wrong for doing so. Maybe they are.
I seriously doubt many GM candidates are saying, "No thanks, I want to fire Cora, and you won't let me. Bye-bye."