I used to work in a company with such a high bus factor that we called "teams" composed of a single people "immortal" like in the movie "highlanders" because of the fact they could not be fired since they were the only people to know how their project works. We went through hard times for the company when several of the immortals resigned one by one. Each time one of us left premises on his last day, we played the song "Princes of the Universe" very loud on the office. I was the last and I left four months ago.