Couldn't you just use the code to do the rest yourself and launch it on your own - write him out of the picture if nothing was solidified legally?
And honestly, even if that wasn’t the case and I could somehow argue that he didn’t own any of the intellectual property for any of the stuff he helped design (which I seriously doubt I could do), we are talking about code that is ten years old by now.
I could always re-design the basic idea and re-code it from scratch, but that is both time consuming and risky (since it would be difficult to completely separate all of the ideas that he might have owned from the ones I had).
I’m currently making good money as a full time salaried employee at a company that I enjoy working at. I’m afraid that the cut-throat, high stakes appeal of a startup is somewhat lost on me at this point.