I believe you're referring to the end times, to the end of the world, which I don't believe will happen anytime soon.
I certainly don't subscribe to any religious superstition, but I don't doubt humankind's ability to end both itself and the world. Some would argue we're already on the brink of doing so:
https://www.bbc.co.uk/news/world-us-canada-64390663
If something is used as the last currency of the world, it will be gold and nothing else.
Circumstances may dictate otherwise. In some post-apocalyptic future, maybe we'll resort to using human teeth as currency. Or maybe it'll be a utopia where we pay for things using time itself as a currency. It's honestly baffling how we, as a species, hold the potential to swing so easily from one extreme to the other. But the fact that something as antiquated as religion is still as ubiquitous as it is doesn't fill me with confidence that we'll end up with an idyllic outcome.