I think that Greece is a potential catalyst for another stock market colapse. The market is massively overvalued, and at the point in one of the longest bull runs in history, investors will pull their money at the drop of a hat. And don't forget that interest rates will be rising soon, so get ready for another bungee jump.
a US stock market collapse? my thinking is that Grexit could cause a massive drop in the Euro, and accordingly, strength in the Dollar. that indeed could catalyze a nice drop in the stock market, as money flows back into less risky assets, like treasuries.
my newbie take on the technicals of the chart is that Euro is actually fairly bullish in the mid/long term. DXY, on the other hand, shows a lot of weakness. while i think a Grexit could cause an initial shock, i think the Euro will likely rally in the aftermath to > 1.14 supply levels.