I was recently introduced to the “lottery factor” as a less morbid alternative. As in, if one of us won the lottery tomorrow and quit on the spot what would happen.
The bus is irreversible and sudden.
I'd say the lottery example works for example with skills/knowledge. ("Do we have someone else who can do what that person was doing?")
While the Bus factor is very relevant for issues like infrastructure and access ("The only person who knew the important passphrase or credentials is now lying dead on the pavement.)
If someone has a lottery factor equal total their bus factor, then you expect them to say “screw you” when asked for help, and you should probably work on that.