As you can see, for the pyramid to progress, you need exponentially more and more people to join. The total deficit rises and rises as you'll continuously have more and more people out money. When they get paid back, you have even MORE people out money. It's unstable because there aren't an infinite amount of people with an infinite amount of money...eventually nobody else wants to contribute, and the system stops, and the nature of something like this is that when it stops, it'll always be at the maximum deficit.
It will never stop. There will always be people investing, more people investing, people re-investing. It is a cycle. People would have to be stupid to surpass an opportunity to double this money.
Of course it will stop. You'll run out of investors sooner or later. It wont carry on forever. You might hope it does, but it wont.