Del. Code tit. 8 § 616
Within 375 days following the date of death of a shareholder, or within 30 days following such shareholder's disqualification to own shares in the professional corporation, as provided in this chapter, all of the shares of such shareholder shall be transferred to, and acquired by, the professional corporation or persons qualified to own such shares. If no other provision to accomplish such transfer and acquisition is in effect and carried out within said period, the professional corporation shall thereafter purchase and redeem all of such shareholder's shares of its stock at the book value thereof, determined as of the end of the month immediately preceding death or disqualification. For this purpose, the book value shall be determined from the books and records of the professional corporation in accordance with the regular methods of accounting used by it for the purposes of determining its net taxable income for federal income tax purposes; and no subsequent adjustment of such income, whether by the professional corporation itself, by federal income tax audit made and agreed to, or by a court decision which has become final, shall alter the redemption price. Nothing contained in this section shall prevent the parties involved from making any other arrangement or provision in the certificate of incorporation, bylaws, or by separate contract to transfer the shares of a deceased or disqualified shareholder to the professional corporation or to persons qualified to own the same, whether made before or after the death or disqualification of the shareholder, provided that within the period specified by this section, all the stock involved shall have been so transferred.
8 Del. C. § 616