>The power was out for days in some places, including mine. My phone battery died after a day, ditto the laptop's battery. My landline continued to function throughout.
In your case PSTN was the "stable fallback" but there is nothing inherent in the technology that makes this so. Your phone stations still need power, and if they don't have backup power they'll be dead as well.
Cables have a bigger chance of breaking if they're in the air, less so if they're buried. Of course, PSTN, power and fiber can all be both in the air or buried. There's nothing inherent in any of them that make them more "resilient". So if you live in an area where your PSTN is buried and your power lines aren't, it might to lead you to conclude that PSTN is "stable", in fact there's nothing about PSTN in itself that makes it so.
In a lot of places, cell towers will have backup power as well, and so will fiber networks, and your power network might be (should be, probably) buried and better protected than your other cables.
In your case PSTN was the "stable fallback" but there is nothing inherent in the technology that makes this so. Your phone stations still need power, and if they don't have backup power they'll be dead as well.
Cables have a bigger chance of breaking if they're in the air, less so if they're buried. Of course, PSTN, power and fiber can all be both in the air or buried. There's nothing inherent in any of them that make them more "resilient". So if you live in an area where your PSTN is buried and your power lines aren't, it might to lead you to conclude that PSTN is "stable", in fact there's nothing about PSTN in itself that makes it so.
In a lot of places, cell towers will have backup power as well, and so will fiber networks, and your power network might be (should be, probably) buried and better protected than your other cables.