Doesn't look like current internet infrastructure could survive, am I mistaken assuming this?
This question is addressed in the book "The Innovators" -- https://www.amazon.com/Innovators-Hackers-Geniuses-Created-R... -- and it's posed something like this: was the internet invented by DARPA researchers who wanted a nuclear-proof communication system which could dynamically route around broken/gone segments of the internet, or by a groups of academic-based hackers at universities around the country?
The answer is... both. Yes, DARPA wanted a self-repairing communications network but the computer hackers at MIT, Harvard, Utah, and the Bay Area would have likely produced something very similar without government being involved. One interesting legacy from the DARPA funding is the RFC nomenclature: the students designing TCP/IP couldn't "specify" anything without risking their funding, so a public "Request For Comment" was a way to publish how they were implementing things -- and how others would need to do it also if they wanted to be compatible.
The ARPAnet was theoretically designed to withstand a nuclear attack. The commercial Internet was not; there are a lot of paths that exist but are not used by policy.
You are right. There are many Tier 1 networks so Internet can’t be destroyed easily. Even If internet dies there’s radio communication and other stuff. Like SATCOM.