Or more likely.. the Bitcoin developers release a new version that allows for more than 21m coins. I think a lot of people don't realize that Bitcoin is still an actively developed beta-version software project. There are several parts of the code that the devs are already thinking about changing (such as the way that transaction fees are calculated, or increasing the number of times you can subdivide one coin). If the 21m limit becomes crippling, I'm sure they will change that too. Really, they can change anything they want as long as they can convince 51% of pool owners to upgrade.