I'm unaware of any collection of humans in history that did not practice some form of religion. I suspect that religion will become extinct only when we humans do too.
But, what may be declining is not religion per se, but rather monotheism. Zoroastrianism, one of the first monotheistic religions, emerged only in the 2nd century BCE. For the entirety of human history before that, about 200 millennia, humans practiced some form of nature worship, ancestor worship or polytheism.
It may be that the age of monotheism is coming to an end, but what comes next is anyone's guess.
The argument still stands. We're still talking about 4 millennia of monotheism, preceded by 200 millennia of various other forms of religion.