Allowing people to be there "strategically" because they are the sole repository of a critical chunk of knowledge or skill is a serious mismanagement failure.

Allowing people to be there "strategically" because they are the sole repository of a critical chunk of knowledge or skill is a serious mismanagement failure. First, it makes the entire company vulnerable to a single accident to any one of the critical people -- massively increases the risk to every other employee and the owners. Second, if a person has deliberately worked to somehow create such a critical niche for themselves, I would make it a critical & urgent priority to develop workarounds ASAP, then fire them. Anyone actively working to create their own feifdom and point failure in your organization is not merely neutral, they have made themselves a direct adversary to the company and everyone who works there. Management needs to rectify that situation, fast.