If BTC not exist one day，then my answer is people will lose total interest in cryptocurrency，it can be interpreted as Bitcoin dies, altcoins die, Bitcoin flourishes, altcoins flourish.
That's right, because the main thing that everyone likes in cryptocurrency is Bitcoin so that the death or life of other cryptocurrencies is also still very dependent on Bitcoin and this can be proven in the decrease and increase in the price of every cryptocurrency that is already in the market.