Shares of Walt Disney Co. closed down 1.7 percent Tuesday in the wake of the resignation of Chief Operating Officer Thomas Staggs, seen as an heir apparent to Chief Executive Robert Iger. The New York Times reports that speculation on the state of the succession is buzzing, with names of possible successors from outside the “Magic Kingdom,” including Facebook’s Sheryl Sandberg and Chernin Media’s Peter Chernin being bandied about.