The unexpected departure of a CEO can rattle a company's employees, customers, and stock price. PR pros say such “surprise” resignations have become more common, and companies now more than ever need to have a communications plan in the event of leadership upheaval.

The seeming increase in these kind unplanned departures reflects increased transparency and accountability around personal and corporate scandals (former Hewlett-Packard CEO Mark Hurd, for example) as well as the increasing stress load of the top job, say PR ...