This is different from battery power, It just needs just enough power to remain on while uploading one video, in the case where someone disconnects the power from a breaker or cutting a wire. It could be done with a small button battery or even capacitor, and would very much decrease an easy security vulnerability.
As long as your internet and WiFi has battery backup too…
That’s already done with a UPS going to my wifi router and cell modem.
Yes. This is common on good dash cams to finish recording to the SDcard when the card is turned off. Wouldn’t take much hardware wise to add this.