My thoughts are to simply wipe the queues and pointers to anything that had been recently played, just in case it’s the middle of the night, or the users are away from Home, as it would reduce the risk of playback starting and perhaps annoying the neighbours. 

That implies a hardware change to all devices, to include a non-volatile memory chip to be inserted in which the source in play is stored, along with this software change to write the data to it. The challenge, of course, is that electrical ‘blip’ you speak of, which can cause substantial challenges to any stored memory, volatile or non-volatile, since there is often a surge / voltage variation that requires additional circuitry to protect against. 
 

Not impossible to do, but I could see the cost of all devices increasing by somewhere in the range of 10 to 25% in order to accommodate these changes. 

I had in mind that the alarm function works in the event of a power cut, the music source is stored and not lost and will be connected to the next time the alarm is triggered.

It should work if the source that’s set in the Alarm settings is available to play, otherwise the default ‘Sonos Chime’ should play as an alternative anyway if it isn’t accessible.