To be truthful I didn’t have a specific technology in mind, though I’d have leaned the way you’ve gone. Pretty simple to increase the resolution by added more surfaces and thus more pulses per revolution. On the idea of a “cheap” pot … be careful as your accuracy is now the accuracy of the pot and it’s reading. I wouldn’t trade a cheap pot for decreased accuracy.
Re: loss of power … I don’t know what more to do than separate the counter circuitry PS vs motor’s and use LV circuitry w/as much holdup capacitance as you need for the former. I guess a good “trick” would be to brake the motor as immediately upon loss of power as it can be detected/confirmed and thus decrease the holdup time needed.