Concerning economic policies, there would probably be major helps to diversification concerning agriculture, as well as industrialization (probably textile, to evacuate all this cotton they produce).
If they are lucky enough they'll learn about the disappearing of Aral Sea before doing anything stupid, and won't kill the Voltas and the Niger for unrealistic agricultural projects. I they don't, well, shit happens, and the government will be blamed (it could become a major crisis)
Also Gambia may become a nest for anarchists, and federalists and other people who want to mess with the Federal government.
The big political issue would be anti-French vs Francafricans, and the place of France in this new situation. Maybe there could be a more successful French Union (even though it would probably have another name) because of more proportionate balance of powers (bigger African States means more balanced power I guess ...)