It's less the "vanishing New York" than the "vanishing self". Lifelong New Yorker weighing in here but the story most people don't get is from the people who've been here _too long_. People that are defeated.
My experience and my experience with most of the folks who've stuck around too long is that the city drives you just a little bit crazy. Even if you're successful in your career here, there is some way that the city has beaten you down (likely w/ family). Most people don't have generations of their family here and those that do often don't share the big ambitions of all of their transplant peers who flock to the city in droves and dominate its population.
Every New Yorker eventually has a time to leave. Most of us talk about how we hope we don't die here.