This is a wise negotiations strategy by the former CEO.
a) Discounts for non-marketability: Most shares in a privately held corporation are purchased at a discount, to compensate the buyer for the non-convertablity of the equity. After all, how valuable would these shares be outside of the family's coffers, especially with decades of in-fighting?
b) Market Value: Despite the acrimonious family history, by making an offer at or above market value, Arthur T. is trying to do the right thing by the Board, by the company and even his estranged relatives.
c) Debt considerations: 50% isn't control unless there's a number after the decimal place. 50.5% will get him back the keys, and re-install him as CEO, but he won't be handicapping the company with extraordinarily high debt service by only seeking 50% of the equity, regardless if he's financing the purchase via a bank loan or through the buyer taking back financing.
d) Zero asset value to outsiders: Outside of the locations the company owns outright or its long term leases, the stores have no value unless a retailing business is looking to acquire some, or all, of the 71 regional locations at one time. This is risky as it's not a national play and in the grocery space, a high-volume, low margin business model.
e) Time is of the essence: For any stores Market Basket rents or has mortgages on, unless they resume normal operations soon, they’ll begin defaulting on lease & loan payments, making a bad situation exponentially worse, not to mention missing vendor or wage payments.
f) Management does matter: If you never paid attention during Organizational Behavior classes, take note now! This unfortunate saga does have a silver lining in reminding all of us that strong leadership, effective management, and a boss who gets to know his / her employees can motivate people at all levels to do their best work.