The Global markets are not going to crash significantly even though Greece exists abruptly. Their is huge liquidity in market which will ensure that all markets (share/commodity) do not crash. Just the money will flow from one asset to other. The liquidity situation is 100 times better than that of 2008. The fed is printing dollars for 4 years with no break pushing trillions of cheap money in markets and same has been replicated by most of the European countries plus China.
Till all this money is not sucked back by all governments out of market people should not panic and sell off. Every dip should be used to buy more. US elections are due this October and Obama will take no chance and advise Fed to pump as much as money in markets they can ( QE3). Stay invested till elections season ends.