Earlier quoted context omitted.
> If quality gets too bad, or prices get too high, someone is going to come and try to eat their lunch. The problem is that in monopoly, things have to be really, really bad and prices must be really outrageous before anything changes. Healthy markets are the opposite - even a minor decrease in value creates a niche that is filled by a competitor.
That really depends on the market. In a market with strong network effects (e.g., operating systems), you are correct. It costs money to switch from windows to linux, and this may preclude a switch for a small cost gain. In a market for commodity goods, this is not true. It costs nothing to switch from Alcoa aluminum to little guy aluminum.
Anyway, it's not as important as when the monopoly is established. Any competition would have to bootstrap itself. Until competition is reestablished, market distortions ensue. They can be as large as the barriers that prevent competitors from entering the market.