Is Greece Too big to fail? will its default trigger systemic risk like lehman brothers did in 08?

With Greece it's more a matter of being too small to fail.

Greece's economy is small compared to that of the 17 country Eurozone so the zone could print more money to pay Greece's debts at the cost of inflation and indeed that's what would've happened to Greece had they not been in the Eurozone.

It's just that the other countries don't see why their citizens should suffer from Greece's poor planning. So now they're laying down the groundwork on how the cost of a countries poor planning will be returned to the citizens of that country instead of to the entire Eurozone. The alternative would be for each country to defer the approval of their budgets to a central authority responsible for the rate of inflation to all 17 countries and they've already decided that each country is to have total autonomy over their budgets.

Countries like Italy and Spain have much larger economies and their mismanagement won't be as easily absorbed as Greece's is so they're too big to be bailed out and the Eurozone needs to have a policy in place that not only works to isolate the other countries from the mistakes of one but gives those economies a chance at survival. Note that this is all the result of a fixed currency, were we still on the gold standard or returned to the gold standard, the problems that Greece faces now would be happening here almost every year.