One of the chief reasons that I do not expect any peaceful “exits” or other secession from long-established national governments is that a successful move of that sort would then have to work pretty strongly to prevent further secession. For example, take California.
Not everyone in California is so deeply offended by the current turn in national politics that they want to break away from the rest of the United States. But let’s say that a majority (or a vocal and powerful enough minority) managed to pull off a vote that passed whatever legislative hurdles it needed to, and was then “generally” supported by the public AND not strongly or forcefully opposed by the federal government. If California secedes, then it’s just as likely that within a year or two, Southern California would then secede from Northern California. After all, once the precedent is established, then what would be the legal hurdle to clear? And I have no doubt that a smaller California would be warmly welcomed back into the Union.
In addition, if Northern California secedes and remains apart from the USA – and wars don’t start nor wildfires, mudslides, earthquakes, volcanoes and tsunamis signal the end of the world – then it’s pretty likely that some communities in that region might feel oppressed by whatever governing body remains (or grows). So there’s no good political reason why individual communities couldn’t also secede from California itself, and unless California wants to call out a state militia (not the National Guard, I guess) to stop them with violence, then who knows where that process might end? Could individual citizens secede as well? Who knows.
The issue of debt is, I think, a red herring. Even the US government will never be able to pay off its current debt, but that hasn’t caused it (yet) to fail as an entity, and dollars are still accepted around the world… for now.
But I led this essay with a prediction about “established national governments”. Since I doubt that the separate European nations that make up the European Union will ever give up sovereignty to the extent that they make the continent of Europe “a nation”, I do fully expect that Union to break down into (at best) what it used to be: a loose association of sovereign nations with lowered trade and immigration barriers among the members. So, who’s first: Grexit? Brexit? Irexit?
I’m betting Brexit… but I’m not betting much.