My theory is that "the new normal" in use after 9/11 is a figurative extension of a therapeutic term referring to how grieving survivors handle the loss of a loved one. From an article in Psychology Today in 2010:
The phrase "the New Normal" is a term from the ‘grief and recovery' world that I've surprised myself by taking to heart. I don't take easily to slogans. If you come at me with something along the lines of "it's all good," I promise you I will snarl. (It's not all good. Some things are less than good. Other things are just okay. Iceberg lettuce, for example, or that brown blouse I thought I liked.) I do, however, feel right at home with diagnostic language, along with family oddities like, "If my grandmother had wheels, she'd be a streetcar." Hence, my fondness for the phrase, "New Normal."
Note that the publisher of the earliest book title cited in the question, The New Normal: How FDNY Firefighters are Rising to the Challenge of Life After September 11, is Counseling Service Unit of the FDNY, 2002.
The FDNY Foundation website describes the "Counseling Service Unit" in an article:
“The mental health of our members is of the utmost importance,” said Captain Frank Leto, the Deputy Director of the FDNY Counseling Services Unit. “Being in this department for 32 years, I know firefighters and EMTs respond to the most dangerous situations, but if they’re having a problem in their family or emotionally, that’s what can stop them in their tracks. We have to make sure that everyone is operating at their optimum level.”
In other words, this early publication with "The New Normal" in the title was published by a unit dedicated to mental health, that would have been familiar with the therapeutic term described in the Psychology Today article above, and the senses in which it was used prior to 9/11 as outlined below.
Many of the uses I found prior to 9/11 fit directly into this sense, and it doesn't seem far-fetched that the sense would lend itself to figurative extension as in "the nation is grieving," hence the explosion in use post-9/11.
Here are a few uses that appeared shortly before 2001.
She said it is her aim to turn those "co-victims" into people who can live in their "new 'normal.' You know you can't go back," to life before the murder, she said. "But that doesn't mean you can't be OK. There will be a new normal. There will be a new life."
Moving backward, there is this use from 1999 that describes its own context:
Those whose loved ones have died will never get back to what Klug calls "the old normal," that is, the way things used to be. "It's a process of moving to 'the new normal,'" he says. The new normal means new habits, new routines.
Another example is from 1996 in the U.K.
The counselors talk about something called a "new normal". The aim for survivors and relatives, they say, should not be to avoid the experience of last April but to minimise the extent to which it disrupts their lives.
Because of the frequency of pre-9/11 uses relating specifically to grieving for lost loved ones, with only occasional one-off uses that are unrelated to grief, my hypothesis is that this term from the Psychology community was adopted to describe the mass-grief of a country following a shocking loss.
Best Answer
We know, not all proverbs have an equivalent proverb in English. But the fun fact here is that proverbs or idioms are created by normal people which later become widely used. So, you can use your awesome creativity to create an English proverb out of the Hindi one.
For example:
Hope it helps :)