Unless there's something special about the EU vs other currency crises that means history doesn't apply, I think it's highly unlikely Krugman lacks understanding of the EU.  Always nice to see that exceptionalism isn't solely an American thing though.

As to the doom scenario, I'd point out that Day One is already happening.  Day Two isn't far behind with unemployment rising at its current rate.

Day Three sounds like projection to me.  They have economic paralysis already, imposed by the Troika.  Your own link in the Day Four section notes economic paralysis resulting in the need to seek oil from Iran.

Day Five is going to be a lot more likely to happen if they continue on their current course.

There are no good options here.  Krugman's pointing out that Greece leaving the eurozone looks like it's ultimately going to be the least-bad option for Greeks.  At least with their own currency, they have some shot at getting out of the hole.  Right now, the EU is slowly bleeding them dry.

Be nice to America. Or we'll bring democracy to your country.