Then I wonder when the Truck Factor applies and if you would always want to lower it. For a few projects I worked on invoking this Truck Factor irked me. A low Truck Factor is insulting to your skills (for you ten others), but a high Truck Factor can be too. Who likes to hear that management is already planning to continue your work after you are found to be roadkill?
I don't even want to hear this metric in a start-up, because how would you even optimize this metric? Be glad you have something worth dying over.