The message you send to the rest of your staff if you let them vest is: I no longer have to work hard, I can slack off and get another job, have some future equity.
The message you send if you just fire without vesting to the rest of the staff is "watch out if I don't like you I will extract work out of them and fire you to avoid vesting.
Both are hogwash.
You are in charge.
That does not automatically make you Mr Nice GUY to all your staff.(though I would hope you are)
Presumably you have employment contracts setting out conditions.
Follow the contract.
Get legal advice. Fire immediately and let them do their worst.
If your employment contract didn't cover confidentiality then more fool you.
If the employment contact allows, fire the guy now, make it a condition of his termination that his/her 'vest" will happen but be held in trust for 6 months subject to conditions of confidentiality etc.
Presumably you have employment contracts setting out conditions. Follow the contract. Get legal advice. Fire immediately and let them do their worst.
If your employment contract didn't cover confidentiality then more fool you.
If the employment contact allows, fire the guy now, make it a condition of his termination that his/her 'vest" will happen but be held in trust for 6 months subject to conditions of confidentiality etc.