I found this article a bit self serving as the author is a "fractional CTO". Nonetheless the problem described is probably all too common. Trying to prescribe a single dose of medicine that cures all patients (and forever) is not possible.

Each situation requires the leadership to assess risks and opportunities with all of their staff, not just John. Accordingly, startups or any company for that matter, should never rely on one person, especially when you are investing many people's time and money in a venture.

Some of the characteristics that the board and CTO may find disturbing in John are probably the same characteristics that have allowed him to create something seemingly of value.

Getting to know the Johns up front, before investing, is key to heading off any potential issues in the future. Knowing what motivates, challenges and more importantly frustrates John will help prevent a meltdown or the need to let him go.

Setting the ground rules up front (for both John and the board) creates an open atmosphere where everyone understands what is expected and what will derail the venture. Revisiting that contract often may also help remind the parties of their mutual goals and their desire to work together.