Ba Sing Se is by far my favorite location seen throughout the series, and lately I've thought a lot about what the city will be like after the War. I've come to a conclusion – the future of the city doesn't look so great. Below you can read my unabridged, uncensored thoughts on why the city's future seems to look gray.
Firstly, we all know that Ba Sing Se experienced substantial growth during the years of the War. Refugees flooded in from all corners of the Earth Kingdom, and quite possibly a few from the Water Tribes (probably not, by I won't exclude it).
Secondly, we know that the Lower Ring is the poorest division of Ba Sing Se, and that it is filled with desperate characters, confused individuals, refugees, and criminals. During the later years of the War, the number of refugees in the city reached its peak. At that time, people were practically living on top of each other, and I'm willing to bet it wasn't always like that.
What I'm getting at is that apartment complexes, such as the one Iroh and Zuko lived in, were constructed for new arrivals to live in. And then there's Jet's tiny one-room apartment. Could that have once been a larger home, converted into a smaller home to preserve space? Quite possibly.
When refugees arrive after a long journey, they'll need services to be provided. Business owners will flock to an area when they know there are hundreds, even thousands of people who need things like food, clothing, and general supplies needed to live. The business owners come in to serve the refugees while they're in town and the population is swelled, but normally, they wouldn't want any part of any area filled with poor residents.
Next, refugees aren't necessarily poor, but they are basically sealed into the Lower Ring for the years of the War, packed in with all of the poorer residents and crime. During the time we see the Lower Ring, you get the sense that it seems like a temporary home for these refugees, or at least I did. My point being, when the War is over, wouldn't you return home where it is safe, away from the crime and poor living conditions? I certainly would.
So I've addressed the fact that most people would leave the city after the end of the War, and what will happen after they leave? The businesses that came to the city to serve the refugees would leave as well, or go out of business, unable to sustain themselves in the poor economy the ring would normally have.
So, empty homes, empty businesses, poor people, criminals, seems like a place that I wouldn't want to live in. This means that the population of the area would go down, rather than go up. As even more people might leave, more businesses will, furthuer sealing its doom.
There's another factor to worry about. Republic City and its growth. As a city with people from all over the world rises in just 70 years, it will undoubtedly challenge Ba Sing Se. With a city like Ba Sing Se, it will be hard to modernize and as much as Republic City without destroying existing structures. Imagine building a freeway in the lower ring, a lot of demolition of buildings will be required. My point here, Ba Sing Se will look a bit dated when compared to Republic City.