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.
Totally agree with this one. We have to consider all possibilities and an altcoin taking over btc is one of those although we cannot say when. And if I were also to chose I'd back up your statement and say that it's either ethereum or litecoin.