I hope you'll pardon me for making assumptions about your age, but if there were one lesson that I could teach the younger generation (or even just my own child), it would be 'assume good faith'.
Because they want somebody out of the company doesn't have to mean that they're shady, or that they're angry. I can think of dozens of reasons why you might want to get rid of someone that wouldn't have any bearing on them personally.
If there's one lesson that I could teach the younger generation, it's that you ought to trust what a person shows you & tells you about their honor and the value they place on their word. When a person shows you who they truly are by acting like this, don't make excuses for them, don't rationalize it, don't give them a third or fourth chance, and certainly don't "assume good faith."
Assuming the best when a person shows you the worst makes you a rube, begging to be taken.
We're not talking about a friend who lied about why he couldn't come to your wedding or babysit your kid.
You don't get more "bad faith" than firing somebody right before you were about to owe them a lot of money.
When a person dicks you over, the best thing to assume is that they are a dick. This not only protects you in the future, it equips you to deal with them in the present. If you wish and hope that underneath they really mean well, you will only be disappointed and ineffective.
If they were acting in good faith, they would have A: fired him sooner, or B: given him the proportional share of what they originally agreed.
Leaving aside bankruptcy or serious, newly-come-to-light malfeasance on behalf of the employee, the only explanation of a firing right before the cliff, AND a disproportionally low offer (just over 25%!), is bad faith.
Even if they decided he's a terrible fit and they hate him, it's their responsibility for not taking action sooner. They need to fulfill their side of the agreement. Otherwise they are bad actors, acting in bad faith. It's just that simple.
NB: when we fired 2 employees who were not working out at all, I paid them both severance, even though I had zero obligation to do so. Why? Because I believe in acting in good faith. Yes, it hurt my business, but it was the right thing to do.
Because they want somebody out of the company doesn't have to mean that they're shady, or that they're angry. I can think of dozens of reasons why you might want to get rid of someone that wouldn't have any bearing on them personally.