In the case of a YES vote it's probably around 20%. In the case of a NO vote it's more than 85%.
Tsipras said yesterday that if Greeks decide to accept the bailout terms, he will resign. Then we will most likely have a Unity Government of centrist parties either from within the current parliament or through elections.
Greece will then negotiate a deal with the country's creditors. The terms of such a deal will necessarily be much worse than the proposal currently on the table, given that the Greek economy and tourism revenues will be down significantly by then due to the capital controls, the political uncertainty and the bankruptcy of the country.
If the Greeks decide to reject the bailout terms, we will probably head towards a Grexit. The government won't have enough funds to pay the pensioners and the civil servants and as thus it'll have to give them IOUs or some form of parallel currency. This won't last for long since the government will continue to only accept taxes in euros and as thus a currency that is not even accepted by the government that issues it will soon be worthless. Greece will default on its debt to the IMF, will exit the bailout program, will vote NO in the referendum and will default on its debt to the ECB. That means that the ECB won't accept Greek bonds held by Greek banks as collateral (or at the very least it will raise the haircuts with which it currently accepts such collateral). Very soon this will lead the ECB to the decision that the Greek banks are insolvent and as such it will shut down emergency liquidity assistance (ELA) to them. The banks will face bankruptcy and Greece will have to recapitalize or resolve them. Since it doesn't have the funds to do any of these, it will have to issue its own currency. At that point it will have de facto exited the Eurozone.
The effects that a Grexit will have on Greece are beyond those of any austerity package could ever have. This new currency will face huge devaluation. There will be double-digit inflation and capital controls will have to stay in Greek banks for many years to come. Due to the devaluation imports will come to a halt. Greece imports pretty much everything. As such there will be huge shortages and the only way to avoid a humanitarian disaster will be to introduce rationing for everything, from fuel to food and medicine. The economy as a whole will come to a halt and there will be a huge drop in GDP. It will take multiple decades for the country to recover to its pre-crisis status.