Detroit is beyond repair. There are other cities in this category, also, but that doesn't take away from the basic fact that the math can never, ever work out for Detroit.
It is a shithole of a city by any metric, filled with festering corruption, shameful public schools (and that's saying a lot given the shameful public schools all over major cities), plagued by neglect of citizen taxpayers, a lack of any real cultural opportunities, and a business-hostile climate.
It should have been forced into Chapter 9 BK a long time ago, but they hoped the casinos were going to bail their asses out, and one of the three casinos is already bankrupt, and the other two are looking so healthy now.
There is no time left. Bulldoze the mofo, change the politicians with a true clean slate, revamp the rules on reception of business, pay attention to taxpaying citizens, wipe out the corruption, run proficient schools, and demand these things, and there would be hope.