For a time, it was the wealthiest city in the world. So yes, the decline was extreme. I don't expect that it will ever be like it once was, but I do think that it will become an increasingly desirable place to live. The changes going on here are dramatic, and as someone from the area, this is the first time that they are indisputably material changes. Despite all the empty space, there is actually a shortage of middle to high-end housing in the city, and the market might be a bit overheated. Demand has definitely out-stripped supply.
So is it safe to say that people are moving back into the area? From when I've visited Michigan, I can say that it is a gorgeous state, and Detroit doesn't look like a bad place to live now. I would give it a shot for sure.