Yes, it will most likely have a huge impact on prices - and the market might take long to recover, but it will not be the end of all altcoins, especially those with products to show (e.g. Veritaseum, Populous, etc.). Most cryptos are not cryptocurrencies, but tokens that can be used to unlock multiple, blockchain-based use cases regardless of the prices listed on the various markets. The use cases are wide and extensive - way beyond the 'store of value' the Segwit + LN hack are aiming for - completely contrary to what Bitcoin is supposed to be, namely peer-to-peer, electronic cash. Luckily Bitcoin Cash (BCH) is going to replace BTC as the real Bitcoin before long (2019-2020).