Forget the conventional wisdom about firing irreplaceable employees. Because if your employees aren’t irreplaceable, you’re doing something wrong. Credit: Gorodenkoff / Shutterstock“The graveyards,” General De Gaulle once ironically observed, “are full of indispensable men.” Maybe so, but the same may not be so easily said about organizations whose success did depend on irreplaceable managers and staff.Take, for example, Apple. Under Steve Jobs it created the iPod, iPhone, App Store, and iPad — products and services that ranged from radical departures to entirely new concepts.Under Tim Cook? What his Apple has introduced to the marketplace are copycat items: A streaming service,...