If they vote "Yes", we will probably see a slow return to normality as banks are allowed access to funding and withdrawal controls are relaxed.
If they vote "No", Greece will remain cut off, the banks will struggle to fund the real economy and the country will fall deeper into recession.
The Government could be forced to issue IOUs in lieu of pensions and state salaries, and we would move closer to the "Grexit" scenario.
But let's put this all in perspective. Greece represents less than 2 per cent of Europe, and 0.3 per cent of the world economy (about the same as New Zealand, actually). Our biggest trading partner in the region is Germany, which takes 1.4 per cent of exports, and the entire eurozone accounts for only 5 per cent of our exports.
My guess is that there will be a "Yes" vote on Sunday, which will keep Greece within the euro and pave the way for a gradual improvement in the situation.
Despite being very small, the situation does pose risks to the broader financial system. It is this contagion, or potential flow-on effects, that have got people worried. However, there are some key differences compared to 2008 when Lehman Brothers collapsed, or to the euro crisis of 2011 and 2012.
Private sector exposure to Greece is much lower today, with most of the lending in the hands of the officials. The ECB is better prepared, with financial crisis-management tools up and running.
Europe is also in better shape economically. We've seen eight consecutive quarters of positive growth and one business activity survey last week posted its strongest reading in four years. Trouble spots like Ireland, Spain and Italy have lower budget deficits, positive current accounts and economic reforms have begun.
The current drama could also reduce the risk of similar issues emerging elsewhere. Portugal, Spain and Ireland are all due to hold elections within the next year, and the problems they are witnessing in Greece might dissuade them from voting for populist, anti-establishment parties like Syriza, the current Greek leaders. There aren't many winners from a "Grexit", and Greece is probably better off in the currency union than out.
The parallel with Argentina is often drawn. They defaulted in 2001 and recovered quite quickly into better shape than before. However, they were also lucky enough to benefit from a strong commodity market.
My guess is that there will be a "Yes" vote on Sunday, which will keep Greece within the euro and pave the way for a gradual improvement in the situation. Relations between Greece and its creditors have been significantly frayed, and political tension will remain for some time. We could even see new elections at some point.
For investors, there will almost certainly be further volatility over the short-term but it is not the time to panic. Greece is small, and the flow-on effects will be limited and manageable.
As is often the case during times of extreme volatility, some time before the dust settles, attractive long-term opportunities will have presented themselves.