He is scummy guy. Ok. Agreed. But like eru said, you make your code available under MIT license. You can't have it both way of putting your code under a license like that and then complaining when someone uses it in a way you don't like. It seems very hypocritical to me to be angry if he is using your license properly. If I put $100 dollar out to charity and they don't use it in a way I see fit, that is my fault, not theirs.
Worst case scenario he makes someone to finish the app and makes a lot of money off it. And then you have a right to be angry if he violated your license in any way. But also you should think that you are very angry because you had app 90% of way done and someone gets all credit for taking it that last 10%. But then that is your fault for not taking it that last 10% yourself.
I will most likely lose all my 10 hn point for this but I would just drop a note to elance and then forget about this issue. Don't be vindictive about this. You are amazing person and have an amazing day, be more happy :) Good luck on being a doctor, forgot about this guy.