If that were the case then options or shares would have a clause stating that they only retain their value if you are still employed. They do not, and for good

If that were the case then options or shares would have a clause stating that they only retain their value if you are still employed. They do not, and for good reason - you paid for them in sweat and opportunity cost, and probably well below market pay, during a period when the company was very risky. The whole point is to be rewarded greatly for that effort in case of company success. It has nothing to do with whether you were employed when the exit occurred.