I doubt that the Bitcoin will be on the second place. I don't think that Ethereum or some other altcoin will take his place. Who the first, that is also the leader. Long time they want to move Bitcoin from the first place, but nobody can make it. There are no bases on it.
I agree bitcoin will be number 1 cryptocurrency for lifetime and no one can dethrone btc in the future because btc is a strong coin that can dominate the market.
I think its not impossible but its not likely to happen. people who try to learn cryptocurrencies first hear bitcoin after that they hear others and because of that most of the people wants to buy bitcoin not ethereum. these keeps bitcoin alive.