Use ATTiny as a battery-backed RAM?
Expanding on my previous comment...


  I need a way to keep an array of memory ignored by the C initializer


You can achieve this by instructing the compiler to store the array in
the “.noinit” memory section:

int my_array[ARRAY_LENGTH] __attribute__((section(".noinit")));


Your array will end up sitting somewhere between the .bss and the heap
(if any), and will not be touched by the __do_clear_bss routine from
the C startup code.


  my question is whether it would instead stupidly try to keep the core
  running when power is disconnected


Most likely. In order to avoid that, I suggest you enable the brown-out
detection by setting the BODLEVEL fuses. This feature of the
ATtiny is specifically meant to prevent the CPU core from running if the
supply voltage is below some configurable threshold.