Im not well read in all and whatnot, but the previous poster is correct.
You have the EU (European Union) the EuroZone, the EEC (European Economic Community) etc. Countries such as Sweden are not part of the Euro or the EEC but are still members of the EU and licensed under the JAA. Norway and Switzerland aren't even in the EU!
Greece may leave the Euro, maybe even the EEC, but they will never leave the EU and hence it should have no effect on flight crew licensing.
DB