This more likely shows poor planning (by the CEO). If your firm is so reliant on one person, even if it is the CEO, it is poorly run. I believe it is a function of a CEO to enact that type of strategy, whether it be succession planning, proper delegation, identifying backups, instilling self reliance, etc.

This probably shows some perverse incentives. A CEO can clearly prove their worth by otherwise sabotaging the firm when they're out.