The shift from open web to closed platforms like facebook and mobile apps might suggest coming end of the open web, but I don't think such prediction is justified.
Facebook as well as other micro-blogging services fill a niche. They provide space for rubbish that nobody else wants to publish. Elite content publishers will never bother uploading their content to facebook and the like. What they will do is to post links to articles on their websites or perhaps engage in some marketing activity that, in the end, drives people out of facebook back onto the web.
Smartphone apps are merely a fad, perhaps a way for OS vendors to cash in on their temporary oligopoly. Market pressure will eventually force them to open up their platforms. Downloading and installing apps simply isn't the user experience that most people are seeking.
The serious problem to be solved here is the vast amount of content that needs to be accessed. Web makes it easy. There is a single distribution standard that is easily accessible. It is unimaginable that all that content gets ported into the world of apps and social networks. Market fragmentation makes it impossible to make all content accessible through all the channels.
While there are generic apps that allow automated redistribution of content through multiple channels, these apps are kind of turning into internets of their own. They function like browsers - oblivious to the content they carry. Nevertheless, usability issues prevent these apps from being a general replacement for the web. One still has to go from one app to the other in rather awkward ways. That's just bad UX.
I see a small drop in popularity of the web, but that's normal as the web gets over its hype period. People who shouldn't have been on the web in the first place are now leaving. That's actually going to help the web to achieve higher levels of quality.
I also see that a replacement for Google search is long overdue. Google failed to hold website creators up to acceptable standards of quality. Google also failed to innovate its search engine. It's still the old list of search results that has been here for almost two decades. Today's data mining technology can do much better job.