20-Year Prospect
Whether you can make it two decades in the B&B business or not will largely depend on the state of the economy. If the national economy is on the upswing, chances are you can get by just fine so long as you're located in a well-traveled area and do your part to provide a great experience to your tenants. On the other hand, if the economy is tanking, it's unlikely you'll be the business of choice for travelers.
That said, the rise of Airbnb and the sharing economy could also present troubles for traditional B&Bs.
While the notion of renting a room in someone else's apartment or home is a fundamentally different business, not often including meals or person-to-person customer service, the main idea to take from the phenomenon has been that people are willing to break away from the traditional model of the overnight-stay business.
That may or may not include B&Bs, but it seems logical that if you're going to try to hack it in this industry, your customer service and guest amenities had better be on point if you want to compete with those prices.