It is the demand which creates the tension and stress. The question is: "Can a 'mom and pop' endure the pressure of increased demand?" You are over simplifying the situation and leaving the human element out of the equation. Business models are just that, models. Personalities cannot be left out of the real world decision which may be required. The pressure may simply dictate that they quit in order to keep the union intact. If "mom" or "pop" are uncomfortable with the increased demand and think that it is time to close up shop, not dissolve the partnership, just simply get on with life after tobacco, what are the chances the business, without one or the other partner, each of which is integral to the sucess of the business, survives.
Further, if one or both see the business as very personal, successful only because of their involvement, knowledge, technique, and "parent" like oversight, the only option is to shut the doors. They are not going to sell their "child" to anyone. All of which was caused by the pressure of consumer demand.
Many MBAs fail because they are unable to apply what they learned to real world situations. One must take what was spoon fed and fit it to work in the world made up of human sensitivities and concerns. Some businesses are not business, they are labors of love. Few MBAs, professors, economists, etc. understand or apply the human element to business.