No, I'm not asking about how you commute... In this context, a Bus Person is someone critical to the busines, so critical that if that person stepped in front of a bus, the viability of the business would be in jeopardy. In my years of working with WISPs I have met a lot of bus people. I get it. Often the business model requires a very leanly staffed organization until it grows enough to justify hiring more help. But I suggest just like you might buy liability insurance or health insurance to protect against expensive catastrophies, an extra set of hands that can take over most aspects of the operation (or more, if big enough), someone that knows enough to deal with an outage without picking up the phone (imagine you are on life support, so the phone is not an option) is also just as critical. Having this person onhand also means that a real phone switched off vacation is possible. You'll come back refreshed and ready to grow your business, and not spend the whole time glued to your email and voicemail. Again, I get it - headcount is expensive. Maybe not trying to hire a ready to go person, but maybe instead growing and teaching someone of a more junior skill level is the way to go.
Give the question some thought - how would my business fare if I were suddenly not able to answer that call or email? If the answer leaves you uneasy, the time to start deailing with this is now.