If you are really a key person in the acquisition, then the whole thing could fall through if you walk away. That should give you a lot of leverage. Speak with

If you are really a key person in the acquisition, then the whole thing could fall through if you walk away. That should give you a lot of leverage. Speak with the CEO and a lawyer to make sure you are represented fairly. "Fairly" could have lots of interpretations here; what I mean is in line with the intent of your original agreement (no shady buy-back of vested options). Negotiating a retention bonus also seems fair.