No it’s not. And this guy is an idiot. NYC has a population of 8.4 million, and 10,000 people joined a FB group about leaving. That’s margin of error. NYC is way too big, too complicated, and too much of a port city, to die.
If someone had said in 1945 that Detroit would be an economic basket case in fifty years they would have been thought crazy. New York will not die but there's a good chance it will experience a steady decline. It used to be the largest port on the east coast but the Port of the South in Louisiana and the port of Houston are now far bigger by annual cargo volume. Having lived in Manhattan when Abe Beame and Ed Koch were the mayor I've seen the city revive but it only really got back on its feet when Rudy took over, he made a tremendous difference. If New Yorkers keep electing DeBlasio or his like its not coming back anytime soon.