Del. Code tit. 8 § 613
If the certificate of incorporation or bylaws of a professional corporation , or a separate contract among all of the shareholders of the professional corporation and, if such contract provides for redemption, the professional corporation itself, fails to fix a price at which a professional corporation or its shareholders may purchase the shares of a deceased, retired, expelled or disqualified shareholder, and if the certificate of incorporation or bylaws or such contract do not otherwise provide, then the price for the share or shares shall be the book value at the end of the month immediately preceding the death or disqualification of the shareholder. Book value shall be determined by an independent certified public accountant employed by the professional corporation. The determination by the certified public accountant of book value shall be conclusive on the professional corporation and its shareholders.
8 Del. C. § 613