I expect that "insolvent governments" refers to the likelihood that a government in financial difficulties will eventually resort to confiscating the assets which its citizens hold in foreign accounts in addition to the confiscation of of domestic accounts, which has already occurred in Argentina in 2001 and in other places. In terms of the rate at which these events happen, I would consider 'once in a lifetime' to be a very high rate given that they can significantly reduce the wealth that you have managed to accumulate from a lifetime of hard work.

People living in countries with poorly managed economies, such as Italy and Spain, should be in the habit of keeping significant portions of their savings in foreign accounts; once the corralito hits, you're already done for.