At the risk of boring the other members, the article is correct in that there are two major distinct but related issues: (1) debt and I would put (2) as productivity.  By borrowing, consumption temporarily exceeded production after joining the euro zone.  For example, 1998-2008, cumulative productivity growth in germany was 22%, france 18%, italy 3%.  Which means that eventually all the factories move north, or southerners have to accept lower wages.  But nominal wages are downward resistant.  

The current discussion is about debt.  Suppose we could solve that - then without similar productivity rates of growth, in order to remain in the same currency, wages would have to continually fall in  southern europe.  I don't think that is sustainable.  

Where I disagree is that the author says the that only way to solve the productivity disparity is via devaluation.  Alternatives: improve your productivity, or lower your standard of living to match your output!  Estonia had a major debt crunch a few years ago from leveraging up as well, but they cut wages and subsequently joined the euro.  I'll bet that they will manage to stay inside it, without a devaluation.  Ireland took some tough measures as well, and they are growing again, and their spreads have come down.  It is maybe too early to definitively say they will make it, but there is a clear difference in discipline with Greece who is still expected, a couple of years into their crisis, to be running a 9% budget deficit!

Early in the crisis germans were talking about helping southern europeans to make their economies more efficient.   That seems unlikely to work: immediately  in greece people were protesting with swastikas on EU flags and bloggers were writing about the fourth reich.  

So my end conclusion is the same as in the article: the two are not destined to stay in the same currency zone.