Much of the internet is both centralized and not. It was designed with redundancies in mind, so it can route around disconnections. The centralization part of it is that services like your ISP generally are very centralized to datacenters, so something "in city" may not be able to be accessed without the closest datacenter or internet exchange being online, each of which has multiple redundancies.

The only good way to do it would be over a city-wide public wifi that has all of the self-hosted information on the locally connected network. Only on that wifi network could you get access, since that system would be linked back to the internet/ISPs via the internet exchange or datacenter.

It would be an ambitious project. The AMPRnet is one such emergency wifi network. It requires a ham license but it's all wifi based long distance communications. The ham license is for authorization to operate on the network, not a legal/technical requirement. They just won't let non-hams connect.

People host all kinds of things on there, so it's fairly robust overall.

As for emergency communications, in an actual emergency (risk to life and limb kind of deal) any person, whether qualified or not, has legal permission to use any radio they find. My family knows this. My concern is that they won't know how to switch to a useful channel when such an emergency happens. I have several handheld radios, so there are a few around that they can grab. If I'm heading out of town with them, I try to bring a few, so if an emergency happens while we're away, I can program and hand off a radio, and we can stay in contact if we need to split up at all during the emergency.

For everyday communications in a primary communications outage, we have some FRS radios which don't require a license. They're much shorter range, but would be useful to have in a pinch.

There's a lot of decent options.

I'm actually looking into setting up a LoRA node, or something similar because there's a spec that I came across for a mail detector IoT thing. It's low power and uses LoRA. It should last several months on a fairly modest battery. It should be able to relay to us when mail is detected so we can go get it from the community mailbox thing when it is delivered. I should be able to tie it into our home automation stuff and just send out notifications when we need to go get it, or change the color of lights or something.

It will be my first step into this kind of thing, so I'll see how it goes.

I'm sure I'll post about it at some point.