The relationship between bitcoin and alt is such that can be regarded that having inverse relationship but that does not mean they can survive without each other. Its true that to majority of people bitcoin is the only cryoto currency but these people only use it as a currency and they hardly play any role in the increase in the market price neither the market capitalisation but those who use it for trades and exchanges so bitcoin can not kill alt no matter how high it goes because they are the ones that give relevance to bitcoin in my opinion and when they are gone then there won't need for exchange sites which will equally takes its toll on the price of bitcoin.