When a member state withdraws from a currency (say, the euro), what can be done to profit from this and who is it that would usually profit? Does any profit require foresight of the event, or can it be made during the event or after?
A pretty good (and easy to implement) play on the Euro failing would be to short the large Eurozone banks, e.g. Deutsche, Suisse, Societe, UBS, etc. In fact, you could short just about any bank in the world, since they're all screwed if that happens. Or you could short the Euro FX market. If you want to get complicated, you can get your broker to engineer a short on Euro sovereign bonds.
Realistically, however, if the Euro collapses, we (the world) are going to be a lot poorer as a whole.