Here is a logician’s or mathematician’s approach to disprove Draghi’s “the euro is irreversible” assertion, with an astrophysics aside.
First question: Do you believe that the euro will exist in 10 billion years from now, with all 18 countries as members? [If yes, multiply by 10 and repeat until credibility is zero (the end of time in our expanding universe is about 10 ^ 65 years), so there is an endpoint, but 10 billion should do it since the sun will be extinguished by then, and probably swallow the earth along the way.]
That is of little practical relevence, but having established with certainty that the euro is going to disappear or break up, use proof-by-induction and contradiction: ask about 5000 years. Then 500 years. 50 year? 5 years? There has to be a death/breakup probability continuum, that begins at 1 (it does exist today) and asymptotically converges to zero. So the euro will be destroyed, for sure, and that reversibility is extremely likely in the next few centuries, somewhat probable the next few years — or possibly weeks, depending on what the Greeks are up to.