In 2022 more than 35 countrys were setting the internet offline - in a minimum of 187 cases. Regional and national.
In a continental and global conflict (war, repression) it is possible to put a lot of people - billions - off the internet. And also natural desasters like solar flares can do harm. The solution of the "byzantine generals' problem" is not an electronic or internet solution.
It's not byzantine generals' problem, but rather problem about communication infrastructure. And node which was offline or disconnected from rest of Bitcoin network can verify block/TX created which created when the node went offline.
It is very interesting to see, that a lot of blockchain developers are working on offline blockchain solutions!
If offline blockchain only means lack of internet, theoretically you could use different medium to broadcast transaction or communicate with other node. An example would be Blockstream Satellite.