Basically, if your car doors rely on the 12V system to open, a bad bump could leave you stuck and unable to open the doors.
Sure, but we've used lead-acid batteries with screw down connectors for decades. How many times you heard of an ICE car which stopped or refused to start because a battery terminal popped off? I've never ever heard of that happening. Far more common is my key fob runs out of battery and I can't figure out the magic spell to get the car started (that happens at least twice a year).
Here's the thing: I think what y'all are most worried about, but you're just not saying it, is being trapped in the car, unable to open the door, because the door doesn't operate from the inside without a motor. Is that really the problem? If so, it's easy to solve: mandate the inside door handle must mechanically unlatch the door. I don't see what that has to do with flush-mounted exterior handles at all.
I think y'all might be thinking that there's a crash, you're unconscious, the lithium battery is on fire, and rescuers can't open the door. Again, solvable problem. They have window hammers and powered snippers, they'll make an opening right quick. In that case, you should plan for the door frame being jammed so all the motors in the world aren't going to get it open, regardless of whether there's power or not.
Honestly, that's a problem with EVs whether or not they have flush handles. A lady and her kid died five miles from my house not more than three months ago, trapped in a burning EV. It's horrible to contemplate. I don't think different door handles would have saved them.