it's true that very few people are truly irreplaceable and it's a good hedge for knowledge to be well distributed. at the same time, small companies rarely have the luxury of employing (and keeping busy) multiple senior architects. unless you're at a very large company, there's always going to be a bus factor somewhere - it's just the reality for 90% of small businesses. either that or you have lock-in to outside consulting companies and services and no one with deep technical insight - just someone who's a consultant coordinator.

i'm not saying it's good to be that bus factor (you're on-call basically 24/7), but it also has undeniable perks for the employee (not the employer).

in reality my bus factor is not that high. the nice thing about well-designed systems is that they seldomly need attention, and there's another dev here who's more than capable of bug fixing and maintaining what's already in place.