You're right. That's true the before the acquisition and after. Your employer can say you have to accept a reduced package or get fired.
The difference is the starting point of the negotiation. If the acquirer wants to keep you, the "right" language in the option plan means the starting point is your original comp package. You have to explicitly agree to a reduced package for it to change. If you have the "wrong" language, there is simply no deal in place to start the negotiation.
The difference is the starting point of the negotiation. If the acquirer wants to keep you, the "right" language in the option plan means the starting point is your original comp package. You have to explicitly agree to a reduced package for it to change. If you have the "wrong" language, there is simply no deal in place to start the negotiation.