If tomorrow is doom's day, end of the world; you pick an espruino system as part of a survival kit, what's your choice?

The problem with ESP32 is regardless of the software on it, it's not very good at low power stuff - you basically have to turn it completely off and lose everything in RAM to get a decent battery life.

I'd suggest that actually https://www.espruino.com/Pixl.js is pretty good, and can run on a LiPo (with the screen on) for months. There's no case supplied but you can 3D print one.

could i connect my bangle v2 's swd out into some bread boards and make it this way?

There was some discussion a year or so ago, and while you can't connect directly, you can use a small microcontroller on a board to bit-bash the SWD protocol and communicate with Bangle.js over SWD - however really it needs its own battery.

... but honestly if you have a microcontroller+battery on a board you might as well just make it a Bluetooth microcontroller and then you can communicate with it wirelessly.