That being said, while electricity obeys the laws of physics, MVA/MVCs throws a wild card into the equation. I err on the side of caution... "Why am I cutting this cable if the vehicle is powered down and stabilized?"
That in turn makes me think about that - was it common during those days to do that, store the keys there? Perhaps for shared service vehicles?
It might've been common in a few American cities Hollywood-adjacent post-WW2 as well, but the accepted explanation is essentially that it's Hollywood being Hollywood - probably that it's a rite of passage as a junior team member to be unable to find the keys and then have someone show you they're in the "obvious" place.
Though I suspect at this point it's a writing shortcut more then anything else: we all know it's a movie, in movie's this happens, and in the plot in that moment you don't want to deal with "can these characters start this car".
yet that's always the most implausible part of the story. Even as a kid, I remember asking "are we the only people who take the key out of the car when we leave? everyone we see on TV seems to leave their keys in the car". If character A just took their damn keys with them... movie would have been over 20 minutes earlier!
And... in murder mysteries... or TV sitcoms... if someone just had a working cell phone, the "communication problem" (misunderstanding or missing) that's at the heart of 90% of plots would be removed and the show would be over. Would definitely make the writers have to work harder.
There's not enough amps available there to do anything serious.
Presumably the driver circuit would notice that no current is flowing from a ruined bulb, try the sparker a few times to restart the arc, then give up and turn off the 90V drive. But it might be cheaper to build…
Keep training up to date. Hybrid HV wiring has a conductive sheath around the actual wiring, separated by non conductive layers. The purpose of this is that when your tool cuts such wiring, it shorts the sheath first and trips a breaker, so that you should be able to cut.
There's a group near here (WA state) that does demos including "throwing" (dropping) battery packs into wading pools while still supplying power, and cutting HV cables on running hybrids to demonstrate this.
But then again, there's near zero reason to do so. Stabilize the vehicle, kill the 12V. Our general go-to? Put the hazard lights on. If you stop the hazards, the vehicle is "generally electrically safe".
Biggest risk that isn't often talked about? HID headlights. Picture being up against the frame of the car. Regular headlights, bulb broken, possibly? Pretty low risk. Broken headlight, and behind it is a high voltage arc? That's a very real electrocution hazard.