Theoretically, it seems possible to run the social networks like Facebook or Twitter in a decentralized way. Much less so for financial payment providers, like Paypal.
In practice, though, only a small percentage of people are technically able to implement such network (or even just deploy), and only a small percentage within those could be able to do it without consulting Internet. Which does not render this idea very viable.
From the other side, we all already have absolutely decentralized and absolutely viable communication network: its protocol is called language. Every normally developed adult can support this network and even teach the others to support it.
Also, although many of us have never spinned wool or hacked wood, we can more or less confidently visualize how such things could be done, recognize when they are being done, and do them if in dire need.
When (if ever) the ability to make a radiotransmitter, a photocamera, or to establish a server for a social network will be like wool-spinning or wood-hacking, then the world would truly become a different place. Or so my wool-spinning-vaguely-aware mind figures.