In my own knowing, I knew that Bitcoin came on the scene the first, and that the idea of it inspired Ethereum second, which gave platform for many Ethereum-based tokens, and there are also other platform-based tokens also like Wave, Stellar, etc
Could all of these starting from Ethereum still exit or useful if Bitcoin wouldn't be any more?
Bitcoin is not only the first cryptocurrency, it's much more than that. Bitcoin represents cryptocurrencies as a concept. If Bitcoin, for whatever reason, disappeared, the whole cryptocurrency ecosystem would disappear as well, for the simple reason that cryptos would no longer be reliable. It would not be the failure of a coin, it would be the failure of an idea.