There actually no other coin can kill bitcoin no other crypto. Why could I say that? Let me say to you that bitcoin is the most used cryptocurrency than any other cryptocurrency since it was started. It is used for different purposes, for example, if you want to invest on some ICOs and they are only accepting bitcoin as an investment, there are also different use of bitcoin like if you want to go some trading. You need bitcoin first before you can buy any other crypto token to hold. And also in gambling, if you want to play some gambling online you need to have bitcoin first before you can play because you will use it as your bet on a particular game.
That it is not true, almost all exchanges that do fiat <-> BTC also allow fiat <-> other crypto, without having to first exchange to BTC. Same argument holds for ICOs, many ICOs used Ethereum as a platform and currency, so you don't have to exchange to BTC at all. And also for gambling there are platforms that allow you to gamble with other coins than BTC (eg: Etheroll).
Bitcoin was the first cryptocurrency but that does not make it 'the one'. Nobody knows which cryptocurrency will be succesfull, if any.. If somebody did know, he'd be quite a rich man
