That sounds insane. Any network other than very basic ones should have physical redudancy, ie. not being in the same duct or even travelling close to eachother. Hell, our local MAN network here does it! Thats in a city with 130k inhabitants, they actually made the network backbone out of redundant rings.
I would hope most telco networks would be somewhat resilient.
A former employer of mine tried to have redundant connections. They had two fibers from two different providers, going separate paths from their Dallas office, etc. However, the 2nd provider utilized a 3rd provider as a regional carrier. And for about 100 miles between Dallas and Chicago, the fibers were run in conduits that were side by side. We discovered that when a single backhoe took down phones, data, etc, to all our southeast Region offices. (it also affected many others). Found out the hard way, that the 2nd providers redundant uplink also went through the same connection. Good luck tracing your fibers all the way from end to end.. Most of this stuff is all contracted to 3rd parties, and most don't want to give you detailed maps.
I heard in this case, both Proximus and Telenet, the main operators in Belgium, run their fibers in the same conduit. So every company thought they were redundant by buing both, but weren't.
I also heard the railways are the main fiber provider: They have long stretches of rail between all major cities, so they are ideal for fiber. But very bad for redundancy
I would hope most telco networks would be somewhat resilient.