Why do you feel that the Nxt blockchain will become worthless?
From what I can see it will be used similarly to Ethereum or EOS as an alternative platform. Given we already understand how platforms are used, in the case of Android and Apple, as well as micro platforms that allow API's for interconnection, I strongly feel in the next 1-3 years you will see much more interconnections between various blockchains to maximize each of their unique characteristics.