wow, you have a lot of knowledge on this stuff.
what do they do if a leak occurs that can not be confined to a small group of students and the integrity of the whole paper is stuffed?
Yeah, it's annoying sometimes, but when it comes to academic matters, I'm the world's biggest dud. But when it comes to administrative/applying for things, things are definitely different.
I believe there would be other security measures in place to ensure the safety of the exam paper. After all, for 10 years since VCAA has been in charge, there haven't been too many breaches in security which indicates that VCAA has a very strict protocol with the management and delivery of exams.
If a very large leak occurred, I believe it would garner a lot of media attention and serious questions would need to be addressed, not to mention that VCAA would be in damage control and their credibility of running the exams would be somewhat tainted. I'd imagine it would be a mess and you can only hope that it doesn't happen (at least not this year for you).