The main thing, is to also make sure his employment file, is all positive.
If he makes a stink about this, it will be put in his file that he is either a bad employee or a troublemaker or disgruntled or not a team player etc.
It will tarnish his current record as a "good" employee. Even though he has "rave" reviews now. And it will tarnish his ability to find another job.
He should, get letter of recommendations, from anyone that he can... just in case. While he is still viewed in a positive way. AND... have his HR department, write him a letter too.
Sad, but it will or can happen.
Also, the company could just let him go... and they can put anything in it as a reason... be it that he quit or that he was fired... or laid-off and it will affect whether he can apply for un-employment or not.
There is only so much an employee can do... legally. If there is "discrimination" that CAN be proven, then an attorney can help. BUT... most states are an "at-will" employer. Meaning they can hire/fire for any reason besides discrimination. Other than that, it can be REAL hard to "prove" that something wrongful is happening. Because, yes, people can lie, and its all about office politics too and personalities.
Unless he had it in writing, that his job position i guaranteed... then I don''t know what he can do. And the Managers and that guy who "took" his position, will angle against him. Legally, there is nothing "wrong" with that... unless there is discrimination cause.
Whenever something is told to him, he should request that it be put in writing. He should be documenting everything.
As his wife, you should not "interfere." Having a spouse call an employer, will not be viewed favorably. It will not help, but probably make things worse.
Yes, it is terrible what is happening.
My Husband, went through something similar. A bad Manager really stirred up things at his employer and was a liar. What eventually happened, is several people were "laid-off." And even though the others knew it was not their fault... the other employees that were not laid-off kept their mouths shut, for fear of losing their jobs, too. So, no one went to bat, for the laid-off employees. It was sad. BUT... it was not 'illegal' and per at-will employment, well, they had grounds for the lay-off. Albeit not fair, nor true. And the Manager, although he is a big jerk and just mean and a monster... could do so. It was essentially a "personality" problem. Not a "legal" problem or infraction. And, HR, had their hands tied. No one, would openly, go against the Manager or the Higher Ups. The manager was very manipulative and covered his butt too. The Higher-ups had no idea... what a jerk he was. To them, he was a "good" Manager.
Also keep in mind, that big Corporations, has their own staff of Corporate Attorneys, at hand. And anytime they feel something may happen... they are already, "ready" and have all the proper legal answers at hand.
All the best,
Susan