Literally bitcoin cannot be destroyed nor created anymore but it can lose its value completely and can become useless at some stage if a crypto made better than bitcoin or no people convert to the crypto currencies or some technology created which can outperform the bitcoin in that case the demand for bitcoin will be none and also the price will become.
That is truth, but i don't believe it will happen in a long long time. It depends in a number of factors to appear and before those factors appear Bitcoin still needs to rise a lot in price and get wide acceptance and adoption before it could eventually be replaced.
That does not mean fiat will disappear in the near future, they will be used together inside the economy i believe.