Earlier quoted context omitted.
If it’s not in writing, it ‘never happened’ - and even then, make sure you have a copy they can’t get at and know your odds of a successful prosecution under the law (and your ability and willingness to see it through). Because sometimes that will be required.
Prosecution for what? Business leaders (and employees) are allowed to change their course of action anytime. I would keep it anyway for your records, due to it helping your claim for unemployment benefits by establishing constructive dismissal as opposed to termination for cause. But it might not work even then.
When changing direction results in actionable torts against employees, then employees are also entitled to be made whole (to some extent).
And I meant prosecution in the sense of ‘driving to an actual successful resolution including getting paid what you’re owed’ - which can be for breach of contract, illegal dismissal, constructive dismissal, etc.
There are a million ways for a company to fire someone without ‘firing’ them, which they’ll often use if they don’t want to pay out unemployment/owed vacation or the like. Many companies will target expensive employees first (age/seniority, expensive physical health issues, mental health problems, or they just think they ‘aren’t a team player’, or are harder to manager. etc.).