Back in the '80s, my friend asked me to check out his car (a '74 Impala) which he was lending to a mutual friend for a road trip.
I had never done disc brakes, and took the car to the tune-up and oil-change shop I'd worked at a few years before for a brake inspection. The owner had dropped the franchise and gone independent, and had expanded into brakes as well.
They put the front wheels on a fancy machine which spun the tires and then measured the efficiency of the brakes when they were applied.
The brakes passed with flying colours, but the brake tech removed a wheel anyway for confirmation.
There was no friction material left on the pad - it was metal on metal, but made no unusual sounds. The brakes still felt fine and performed well.
I took the car home, and did my first disc brake job.
All that to say, it's unusual but not impossible for brakes to be shot without any symptoms.
However, I can't imagine a worn-through rotor not sounding and feeling awful.