Well... the immediate effect on miners alone would be such that the price will go up due to lack of miners, creating more scarcity. The dam provides a great deal of power to a great deal of CCP mining operations... as well as all kinds of other weird stuff. Loss of life... destruction of property... the economy actually likes these things. There might be a blip and a dip, but it wouldn't be long before the world markets moved in and generated profit from rebuilding. But, if the thing collapses overnight, I posit it would be wise to watch for a spike.