I agree, It is unlikely some deal required Nader's

I agree, It is unlikely some deal required Nader's removal as a request from the other party. However if a deal is in the works and Nader flatly refused to accept it and the rest of the Board wants to pursue the negotiations, the board may have decided to let Nader go so that hurdle is removed.

totally a guess, and I do think Nader was removed due to missed goals and nothing more.