He had a legal contract and was terminated for not agreeing to a new contract...seems clear cut to me.
You are deeply invested in a certain view of contract, as evidenced by your equating plant closure (Republic Window moves to Iowa); Feilbogen; and now DeSantis. Given the superficial and simple-minded analysis demonstrated by that, I would expect everything to be perfectly clear in your mind.
But every well-conceived contract includes a considerable amount of language describing the outcome, should "plans change."
Perhaps he was in a situation where he could have been terminated without cause (subject to any commitments made by contract, pay due for days worked, COBRA rights, etc.). AIG could have fired him, but decided instead to offer him a job in a different unit. Maybe he's a non-performing employee.