Bus factor is irrelevant.

It's a concept that basically boils down to "people would not be smart enough to understand the code unaided". This is plainly wrong. I speak from experience of diving into some horrible code base.

It also assumes that reproducing the functionality from scratch would be hard. Looking at all the reimplementations of A where A is one of unix, X, web browser, network stack, SQL database and other complex techno, it is also clearly not true.