No, you shouldn't accept this deal. You are not willing to give up your territories and the culture of your ancestors so easily!
Meet with David II and once again use your skills of diplomacy to try and come to some sort of arrangement. Let him know that you desire peace. If you are allowed to continue ruling peacefully in the west, you will be no threat to him.
Why hang around waiting for David II to strike first? You know you are not part of his vision for Scotland's future. Attack his kingdom. Let him know that you are indomitable. He will be too afraid to bother you!
Which card will you play?