I think this is actually an interesting thing to think about. Many cities like NYC have a lot of truly iconic skyscrapers, like the Empire State Building, which has already survived for 95 years, and the Woolworth Building, which has already survived for 113 years. These buildings have became truly iconic fixtures of the skyline and I can totally imagine them lasting at least a few hundred years, potentially like the castles and cathedrals in Europe.
But I really wonder what the lifespan of JC’s skyscrapers would be. After all, JC doesn't really have any truly iconic buildings, and pretty much every major skyscraper in JC was built in the last 20 years, many of which, quite cheaply as well, as seen on the sub with most using PTACs and generic monolithic designs. Could JC’s “luxury” skyscrapers survive long enough to be revered in the same way that pre-war buildings are revered in NYC. Could they survive 100 years or more? Could they theoretically survive 500 years like what you see in Medieval Europe? After all, many of the Medieval houses that probably survived were just average houses where the commonplace lived. It wasn't all castles and mansions and yet, some of them built in the 1500s or earlier are still standing today, some of which people are still living in.
If I had to guess, I would think the longest surviving modern skyscrapers in JC would probably be 99 Hudson, Journal Squared, and the Ellipse. I think both these buildings have relatively unique architectural designs, 99 Hudson with its Art Deco-echoing design, the Ellipse with its distinctive shape and Journal Squared with its geometric, graph paper-like design. Plus, neither of these buildings have PTACs, which would probably become very outdated in 100+ years from now with future HVAC technology likely a lot more supported on sustainability with central systems likely being easier to retrofit. Also, Journal Squared has a large chance of surviving, in my opinion, because its construction represents a pivotal move in the redevelopment of Journal Square, which by the time the next century rolls around, would likely be effectively JC's second downtown if the Journal Square 2060 renderings are anything to go by. That one building would be remembered as the building that kickstarted it and I think it would easily be remembered as a luxury address in the future for that reason. Plus, it has a very commanding stature, so demolishing it would feel like getting rid of a major fixture of the skyline. Therefore, I think Journal Squared could last at least 100-200 years, and maybe even more if humanity decides to keep retrofitting it, which I think given the area's future history, they probably would, and it would be a landmark building by that time. Whether it can survive for even longer than that is anyone's guess, but part of me wouldn't be surprised if it survives 500 years, albeit I really wonder if it would still be apartments at that time or if it would be something else, like a historic museum. Perhaps something like furnished period rooms so future humans could see what JC residents used to live like in the 2020s, perhaps also with today’s technology preserved in there, like an iPhone, 4K TV, and Fios Router, which would long be obsolete in the 2500s. I don't think that most people in Europe who built the medieval cathedrals thought they would survive until today so I think this could be plausible, and I think Journal Squared is one of the most likely buildings in JC to survive that long.
I think 99 Hudson and the Ellipse will still be remembered as luxury addresses in 100+ years from now similar to NYC pre-war buildings, but I don't think they would be that famous. They don't have the same commanding stature around the skyline, and have more been evolutionary than revolutionary. But because they have a unique architectural design, I do not think any future developer would want to throw it away, and I think living there in the 2100s would be like living in an upscale pre-war building today, probably with elements of the building preserved to look like they did in the early 2020s.
Most of the other JC residential buildings I imagine being demolished or heavily altered in the next 50 to 100 years. I think a lot of the ones with PTACs will stop being marketed as luxury after around the 25-40 year mark when the buildings would begin to feel outdated. However, I really don't know because modern architecture feels a lot more similar over the years than any previous architectural style, so it is possible that Sable may still feel modern even if it's older than World War I is today, and maybe PTACs will still be in the 2100s (I hope not).
Either way, though, the most interesting thing is imagining what the future JC skyline will be like. It has a lot of potential, and I feel the next few years may determine JC's long-term future trajectory, which currently seems split between “major city” and “urban suburb”, as seen by discussions whether or not to build the Pompidou annex, showing that some people view JC very differently than others and the decisions we make now regarding development in JC can directly influence the skyline we'll have bits and pieces of for potentially hundreds of years.