I doubt the #2 coin based on market cap will vanish any time soon. There would have to be a monumental failure for such a thing to occur. Even then, it is likely to have code forked and altered from a state from before, giving it continued life.
That's correct. Ethereum has been the largest cryptocurrency in the market next to Bitcoin. It's quite impossible for it to vanish or disappear anytime soon because there are a lot of investors on it, and a vast number of people supporting it. For it to fail, something catastrophic would need to happen. But, given that developers are quite active on the Ethereum project, it's very unlikely for such event to occur in the future.
Even with the DAO hack back in 2016, Ethereum has survived and remained as the second largest cryptocurrency by market capitalization. The hard fork of Ethereum Classic had no effect over Ethereum's existence and longevity, meaning that it's difficult to take down easily. But one thing for sure, is that prices are falling. This could be temporary, as a result of Bitcoin's decline across the whole crypto market. In effect, if Bitcoin's prices become cheaper, so do Ethereum's. There is a lot of potential for Ethereum to grow into a solid platform for smart contracts as it scales with its Plasma Framework and Raiden Network upgrades.
Therefore, Ethereum will not vanish but will grow in terms of price, and community support in the future.