Extension of this question.
The micro-controller in question has an internal RTC module but no VBAT pin. As such, the only way RTC can be given power backup is to use a battery for whole microcontroller, sense the absence of main 3.3V power supply and shut down the micro-controller leaving only RTC running. However there will be external LEDs and other elements present which might draw current from the battery draining it quickly.
Top answerer of that post hinted towards a minimal circuit using diodes. However I couldn't come up with a simple solution. If the circuit is too complicated and/or costly, it might be worthwhile to select another microcontroller which has a VBAT pin.
Is there anything that I can do in this regard?
I am looking at CR2032 battery for this purpose. However I am also leaning towards using a supercapacitor for the same purpose. Max duration of power outage will be 6 hours and I think I can easily find supercaps which will provide power that long. If I fail, CR2032 is the way to go.