From the article you linked: "There is a rare alternative definition for the bus factor, namely: the number of people who are indispensable for the project. In other words, it is the minimum number of people who are a single point of failure. If using this definition, then a high bus factor is considered a bad thing (since the loss of any person included destroys the project), and zero is considered the ideal bus factor."

Perhaps "bus risk" would be a better term for this usage?