Without the Internet, my ability to communicate here would be reduced to printed pamphlets and receiving radio broadcasts.
In the great 2003 power outage in eastern North America, there were already problems communicating with people about the outage because a surprising number of people didn't have battery-powered radios. Kill the net, the phones, and cable TV and that cut off the majority of people 15+ years ago.
When the 2013 ice storm hit Toronto, entire neighbourhoods were in the information-dark after the backup generators for cell towers died. It wasn't long before my neighbours came knocking asking if I knew why the power was out and what was up. Phones were down. TV was down. Internet service was down. And they had no other way of getting information. I think I might have been the only person on the block with a battery-powered radio.
Fully decentralized services don't make money, as they inherently rely on a population of providers to be exactly equal to them.
After Usenet fell out of favor, RSS sort of answered the mail here since aggregators could pull the news together and cache it. That is, until news services stopped providing more than the intro paragraph in their feeds.
But yes, social networks are central to many peoples relationships now and people would have to remember how to communicate without messenger apps again.