As founders you're no doubt driven people, it's what it takes, but you can't expect everyone to share your vision, or be able to give up their time or commit their future for something they didn't invent - even if it starts to take off - simply because it isn't their idea no matter what the incentives.
That said, perhaps what you are looking for is someone who fires on all pistons, and surely you can spot that in the recruitment process. The twinkle in their eye, the energy, whatever it is there'll be a clue.
Also have you tried breaking down the tasks into smaller tasks, maybe the sheer size of the project has overwhelmed him. That way you get to keep a good handle on progress and can easily switch to someone else if things go wrong.
Talking of which, you'll be surprised how many good programmers can pick up the ball and run with it, so don't feel tied to this one guy just because he has all the knowledge.