The economy is a system which seeks out a stable balance, and when you manipulate the system a series of cascading unintended consequences change where this stable balance will be found. The problem that is at the core of any potential recovery for Detroit is that the majority of potential employees are less educated (combination of poor graduation rate and poor quality education), are less reliable (combination of drug use and high crime rate), and expect dramatically higher wages and benefits (due to unions) than other regions within the country and other countries around the world; and, to make matters worse, a company would have a much higher tax rate to set-up shop in Detroit.
At this point in time, the best option to "Fix" Detroit involves the government buying all available land and demolishing any buildings that stand on it, creating "Right to Work" legislation along with cutting spending and taxes, and doing a multi-year crackdown on crime. Realistically, over a couple of decades the government would make a fortune off of the land because as crime disappeared and companies returned the land would rapidly become very valuable.
