Ethereum or Litecoin would probably take the place of bitcoin. If bitcoin were to die tomorrow, it would probably drag down the altcoins with it as well, but if you give altcoins some time until they can establish themselves, they wouldn't be harmed in my opinion. An altcoin may eventually take the place of btc as the best crypto as well, especially considering the scalability issues that btc might face in the near future.
i heard that some of the bitcoin users have lost their interest,because they hear from others that bitcoin price will be going down,but we have to explain to them slowly that in that case we know that bitcoin price will come back in just a few days and we know that it will go up again.so guys don't lose your hope just continue your play in bitcoin never lose hope.