Do any of these fancy frameworks actually make a HTML fallback anymore? Most of the web pages I visit still renders fine without javascript.
Having said that, it's entirely possible (though not easy) to have your React app work without JS enabled by rendering it on the server before sending the page to the client. This way, you get the best of both worlds, but it's a lot of work to implement this properly for a remotely complex app. The answer in the short-term is that you shouldn't be using a "fancy framework" for anything for which the above disadvantages are a deal-breaker (like most public sites) until the server-rendering story matures and becomes more compelling.