I like the point made in this piece on Steve Ballmer's legacy at Microsoft about how often the direct impact of CEOs is overplayed:
'The most common, almost universally accepted reason for company failure is “the stupid manager theory”. It’s the corollary to “the smart manager theory” which is used to describe almost all company successes. The only problem with this theory is that it is usually the same managers who run the company while it’s successful as when it’s not. Therefore for the theory to be valid then the smart manager must have turned stupid at a specific moment in time.'
The role of CEOs in the success or failure of businesses is clearly important, but it's not the only factor. I often think that a big part of the role of a CEO is to set the conditions under which the organisation (and the people in it) might flourish. The interesting exception is perhaps the Founder-as-CEO, where the role they have in establishing the fundamentals of the organisation (culture, values, vision, strategy, initial processes and practices) is so elemental that they are intrinsic to the success or failure that then results. All of which makes it very difficult for the successor, whose reward and incentives are likely be focused on building sustainable growth, to avoid the innovator's dilemma and disrupt the very thing that has been so fundamental to the company's growth and success thus far.