Warren is just a person afterall, he does not know everything. Bitcoin can indeed be replaced by another cryptographic currency but who knows.
There is that possibility... But I think Bitcoin will always remain relevant and maybe even used in a "gold standard" type of way...
When other cryptos offers more promising/beneficial features.. It may surpass Bitcoin in purchasing power a little bit, but each crypto will always be compared to the purchasing power Bitcoin holds... Especially after the fiat system has been replaced and we will no longer compare bitcoins purchasing power in terms of dollars.