RF modules (LoRa et al)

As far as STM32 and sleep, you can still do pretty well - nothing stops you from waking from sleep on an interrupt, doing stuff, and then going back to sleep without Espruino running - which should still be pretty efficient especially if you can do what you want without powering up the external high speed oscillator.

Still, even having some basic decode in the receiver and a tiny FIFO (so no packet handling or anything) would bring the power consumption down drastically.