One known cataclysm that could make the whole interruption of all the telecommunications but also every electricity network is a Major big Solar storm that hits the earth!
But what about Bitcoin..? In such case the bitcoin network would be paused, not all at once., some nodes before others.. Gradually, following the interruption areas of the internet!
When the whole world have big problems with complete Internet shutdown, there are globally issues that bigger than Bitcoin mining and Bitcoin network. It can possibly be a catastrophe or even more terrible than that, like an apocalypse and massive living organisms on Earth will be at very high risk of extiction.
If the future is not too gloomy like this, Internet won't be shutdown globally, and from cable Internet, we will be able to use alternative Internet like Satellites.
Bitcoin blockchain will continue moving with new blocks and Bitcoin mining will continue solving new Bitcoin blocks and transactions.
[Total privacy Bitcoin]: off grid Transactions LoRaWan/goTenna.