The comparative constitution’s project shows timelines of the world’s constitutions. Japan’s constitution appears as one of the most stable ones, Switzerland’s doesn’t.
The constitutions of 23 countries specify how territories may secede, according to Constitute. Here is the clause from the Liechtenstein constitution:
Individual communes have the right to secede from the State. A decision to initiate the secession procedure shall be taken by a majority of the citizens residing there who are entitled to vote. Secession shall be regulated by a law or, as the case may be, a treaty. In the latter event, a second ballot shall be held in the commune after the negotiations have been completed.
The Economist discusses the life span of constitutions. 19 years.