I once had an aftermarket brake pad delaminate from the metal backing plate.
This was on a rear wheel. There was an immediate and significant loss of pedal and braking ability - and I still had a good size metal plate as a brake pad to rub against the rotor.
It’s hard to imagine a vehicle with missing pads even stopping, much less not making all sorts of noises as the caliper assembly and piston grinds itself away on the rotor.
I’m surprised the piston didn’t pop out of it’s bore with all the extra clearance.
Perhaps the brake modulation system on these very new vehicles tells the still functional pair of brakes to kick in harder. But it ought to also turn the instrument panel idiot light on. Being found in a rental car, the average customer probably isn’t going to care if the instrument panel lights up like a Christmas tree, as long as the car still goes. A person who purchased the car would care more.