If the Greek people vote no, what more would be needed for them to be dropped from the eurozone?
As I understand it, the referendum isn't about whether Greece should stay in the Eurozone, but purely about whether the bailout should be accepted. Following a no vote, Greece could still hope to achieve a new, gentler bailout agreement, or perhaps default while remaining in the Eurozone if that is possible.
Exiting the Eurozone upon default would have certain benefits, though. The risk of over-inflation is real, but doing away with the Euro will open up chances to grow the economy with exports and tourism. If Greece chooses not to exit, they'd still be under the heels of German and French banks. Defaulting and exiting from the Eurozone is their best option, in my opinion.
Check out the link I just contributed to the thread. Stiglitz can explain it better than I can.
Officially the referendum is only on whether or not to accept the proposed bailout. However, the leaders of many of the other Eurozone members have said that Greece will be able to keep the Euro if and only if it votes yes, so there's a good chance Greece will have to leave the Euro immediately after a no vote. The Greek government has claimed that they will have a new deal within 48 hours of a no vote, but it's not entirely clear how they can achieve this.
Greece would need to decide to leave by themselves. What other countries can make is create conditions to make it undesirable for Greece to stay in the euro, but those kind of measures would probably make the interest rates of weaker Eurozone economies balloon, as it will make it clear that the Eurozone will not be solidary in this situations, and it could even unravel the euro as countries start to leave the euro in a domino effect.