Today, the New York Times carried an article about some of the issues which would arise if Greece drops the Euro. There were many listed, and they were horrifying. It also points out that planning for it is being discouraged for fear that would make it more likely. Yet, it is clearly Top Management's fiduciary responsibility to do so. If they do not, and it happens, they could be held legally responsible for any negative results.
One of the most uncertain in size, but inevitability in occurrence is fraud. Any sudden realignment of currencies (and it would have to be sudden to prevent flight of capital), would provide enormous opportunities to fraud rings. Most current fraud prevention methods would be helpless as they could not act fast enough. Billions would be lost by the companies that engage in business using Euros. Few have considered this as the fragmentation of the Euro looks very possible.