I don't exactly agree with its premise, that Cantonese is being "swept away". Hong Kong has for it entire history has dealt with the seemingly always looming threat that the Cantonese culture and language is going to be eradicated by mainland Chinese influence, or some other global trend.
Three years ago, I moved into my first solo apartment in Hong Kong, and it was right across the school. I absorbed A LOT of Cantonese because in Hong Kong the teaching method is basically call and response learning -- you yell Cantonese words into a megaphone and wait for the children to shout them back to you.
Cute. But not at 8.15 am, long before I want to roll out of bed and go to work.
Having lived in Hong Kong, I can tell you that Hong Kong is a neighborhood language, spoken by a HUGE diaspora of Chinese immigrants who fled China or moved to the United States, Canada or other "western" countries in order to find a new life. No matter how many years these people will live away from Hong Kong or Guangzhou, it's my understanding that speaking Cantonese is a way of life.
So is the debate about the dialect's sustainability. Hong Kongers come from a place that is always rapidly changing -- the dialect itself is immensely fluid and flexible. There are young speakers of Cantonese today who speak a version of Cantonese that their grandparents don't even understand, and vice versa.
I think that the speakers of Cantonese in New York must be behaving pragmatically. It makes total sense to know Mandarin if you do business with China. And every country on earth does business with China.
Here's the link again: Learning Chinese in New York
Cantonese, a dialect from southern China that has dominated the Chinatowns of North America for decades, is being rapidly swept aside by Mandarin, the national language of China and the lingua franca of most of the latest Chinese immigrants.
The change can be heard in the neighborhood’s lively restaurants and solemn church services, in parks, street markets and language schools. It has been accelerated by Chinese-American parents, including many who speak Cantonese at home, as they press their children to learn Mandarin for the advantages it may bring as China’s influence grows in the world.
When I was in China Town, I also heard Shanghaiese, Yunnan dialects, Taiwanese mandarin. But you also hear this in China, and in Hong Kong.