Of course there would have to be two currencies but not by going back to their old currencies. Just a secondary currency introduced which could have different levels aginst the euro while enabling a return to the euro once alignment is achieved.
As AK has said, all that's really necessary is for the weaker members to clean up their act. They are in fact very rich and successful economies, but damaged by corruption and mismanagement.
If the Italian establishment ran Germany, that would be a basket case too. Conversely, if Italy was as law and regulation abiding as the Germany, they'd have a very successful economy.
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That's only fiddling with the issue. The big problem for euro is simple fact it is not a centralised fiscal system. Taxes benefits etc etc are collected centrally in USA distributed accordingly. Prevents spiralling down of poor performers. Eg. A firm goes bust in Alabama, its work force are effectively paid from taxes on California. In effect its a redistribution of wealth. In case of Greece they simply rely on short term hand outs with conditions. (ie Austerity) Folk in Alabama can jump on a bus and work in California with no language issues. It's a centralised work force. EU is not.
EU needs to be a centralised system with one Sovereign control. It's members will not give up their control to let system work.
It (the Euro) is doomed one way or other long term.
EU contains 28 automonous Countries with 28 disparate fiscal policies. USA has just one. Yes, the individual states have lots of freedom within set limits but ultimately answer to a single government. Personally don't think the half way EU is trying to operate actually can.
I, d actually support the a complete change in system to become a full USE, with a single fiscal policy, central taxes and centralised welfare but that in reality is not on offer.
USA went to war with itself to get it.