I was told years ago that if there is not a male heir to the throne (is it a throne? my mother told me the Grimaldis are not royal, that they are "serene highnesses") Monaco will revert to France. Does anyone know if this is true? It is not addressed in the article.
I can't say for a fact, but this was discussed in a different thread last week, and I believe that Monaco's constitution was amended to allow succession to other than a male heir.
Maybe you could find something more specific on Google.
Prince Albert, 47, who has succeeded his father, shows no sign of marrying or producing an heir. This would previously have led to Monaco becoming part of France once again, but the constitution was changed to allow his sisters, his aunt and their descendants to succeed.