The same thing with the factory, the more products he makes, the more interested, the better he improves the quality of the product, the owner of the factory there is no reason to close the factory (unless the product is not desirable anymore).
May not be irreplaceable because Bitcoin is The first digital currency to implement the full cryptocurrency protocol, the security, integrity, and balance of all ledgers guaranteed by a bunch of trusting parties . because , I think it's never too late to start investing. I think all currencies including digital currency will decrease, but it will not go down drastically .