I skimmed through the article and I believe it might be true. And yet this doesn't mean it's the end for these coins, just like you say. Firstly, not many people are going to trust this info and believe there are some unsolvable security problems with these coins. Secondly, other projects in which these coins will be involved will help to maintain the price. For instance, a chain of cafes in my country is planning to accept dash as a payment. This may lead people who have very limited understanding of cryptocurrencies and don't care about anonymity use it.