So i'd say, its reasonable to go abroad, to abandon home and make something of life, when you have a chance to do it. And later, if you still feel close to your home, you can return and create something that makes sense for you, with confidence and resources. The root causes, why areas went bad, may have died and there might be space and hunger to grow something new. That is at least my colorful narrative.
I work with many people from so considered poorer countries. They all miss their homes. But actually no one ever said, they want to go back and build something. :)
I think there is no obligation to stay at one place and make it work.
Of course, it depends on ones nature. I have friends who miss and pine for their home country and do end up going back. Others like myself enjoy our new lives and identities in the US and stay.
In a way, I think, this is precisely what the discussion in this thread is about.
On an individual level this might make sense, but if everyone does this, it just amplifies existing problems. In the city you're leaving, inequality would just grow worse, there would be a brain drain, and family support structures would weaken. In the city you're going to, housing costs would go up, and pockets of area would be insulated from the wider reality of economic decline. This would cause areas of the country that strongly vote one way, and the rest of the country would vote the other.
Instead of encouraging people to just move, why not encourage people to stay and help those who are experiencing a declining quality of life? It would accomplish more than just leaving to "reputable," aka "rich" cities.