FFS. I think people must just prefer to wallow in ignorance than apply a modicum of common sense.
330 million people are using the euro everyday across 17 countries.
If it was about to collapse completely we could expect to buy 5€ for a quid, instead people continue to moan that at 1.19 the euro is still way too strong.
If Greece did leave, it would introduce a new currency alongside the old. Just as the introduction of the euro here in Spain ran in parallel with the peseta, so would a new drachma be introduced alongside the euro. The new drachma would be pegged to the euro for months, possibly years, just as the peseta was pegged at 166 to the euro. It wouldn´t matter a fig what letter was on the euro notes, the Greek banks would change people´s money into the new drachma as and when required.
An orderly conversion is in absolutely everyone´s interest, the ECB's and the Greeks.
For the Greeks, after a long period of transition, refitting cash points, printing new currency, converting bank accounts and mortgages to the new drachma, upgrading the software on tills, bar code readers etc etc It would finally end the peg to the euro and float on the currency markets.
For the ECB and the remaining 16 nations it would probably be barely noticeable. This rubbish about the "Y" serial number is just nonsense, the very worst type of scaremongering. Again, 330 million people using euros, Greece have a population of what, just 10 or 11 million? To suggest that the remaining 320 million people across the EU would have to spend the next 10 or 20 years examining bank note serial numbers is just ridiculous. Automated machines do not read serial numbers on notes, so every train ticket dispenser, vending machine across the continent would immediately be rendered useless. The cost would be galactic. Instead the notes would continue to circulate as before because they belong to the ECB, not to Greece and as I´ve said countless times before, it is just paper, it doesn´t represent gold or holdings in a bank or anything else, because that is how fiat money systems, pound / dollar / euro work. The only thing that gives the euro its value is the confidence that people place in it. The letter "Y" on it counts for nothing other than to identify where it was manufactured.
Again - the Greeks do not own the euros they print, they belong to the ECB, the currency belongs to the ECB, a euro, is worth a euro.
If the UK were to join the euro, it wouldn´t buy euros with pounds, because that wouldn´t make sense. What would the ECB do with a warehouse of sterling once the UK had made the transition? It would be worthless as it would be a dead currency. A warehouse of toilet rolls would have more value.
Finally, physical cash makes up such a small percentage of any currency as to be almost negligible. Fractions of 1%, a number so small that it has hardly any influence on exchange rates. The real euros are in mortgages, savings, property etc.
However, if people want to peddle rumours, scaremonger, generally waste their time fretting over hypothetical, non-sensical scenarios then of course that is their right. By all means check your serial numbers, make sure you don´t have any notes with a Y on them if you need a taxi in Berlin, and don´t try and buy a litre of water in Rhodes with a 500€ note because they might refuse to accept it. And do buy US$, with debts of 13 trillion, several states technically bankrupt, and a cracking policy of quantitive easing to devalue, the US is certainly blazing a trail for the rest of us.