Well... they wouldn't be the first ones to black out the Internet either. And I'm not just talking about threats specific to oneself here because that is a much different threat model, but the effects of being collateral damage as well. Say, your country's leader says something that makes the US President cry - who's to say he doesn't order SpaceX to disable Starlink for your country? Or that Russia decides to invade yet another country and disables internet satellites [1]?
And it doesn't have to be politically related either, say that a natural disaster in your area takes out everything smarter than a toaster for days if not weeks [2].
> If your BIOS or bootloader is compromised then so is your OS.
well, that's the point of the TPM design and Secure Boot: that is not true any more. The OS can verify everything being executed prior to its startup back to a trusted root. You'd need 0-day exploits - while these are available including unpatchable hardware issues (iOS checkm8 [3]), they are incredibly rare and expensive.
[1] https://en.wikipedia.org/wiki/Viasat_hack
[2] https://www.telekom.com/de/blog/netz/artikel/lost-place-und-...
Then you tether to your phone or visit the local library or coffee shop and use the WiFi, or call into the system using an acoustic coupler on an analog phone line or find a radio or build a telegraph or stand on a tall hill and use flag semaphore in your country that has zero cell towers or libraries, because you only have to transfer a few hundred bytes of protocol overhead and 32 bytes of actual data.
At which point you could unlock your laptop, assuming it wasn't already on when you lost internet, but it still wouldn't have internet.
> The OS can verify everything being executed prior to its startup back to a trusted root.
Code that asks for the hashes and verifies them can do that, but that part of your OS was replaced with "return true;" by the attacker's compromised firmware.