They should have done whatever they could to keep Zuckerberg. They had their rockstar who could execute, but they couldn't keep it together. Oh well, they still got a lot more money out of the deal than they would have had Zuckerberg never entered their life and had their app built by another developer.

I'd say a standard well written NDA that specifies the role of Mr. Zuckenberg would be sufficient to take over a significantly greater role in FB. So, a standard NDA - very simple yet very effective in making sure your disclosure enjoys a good level of protection.