Seen rotors like that before but never a missing caliper. Neat.
It's actually possible it stopped somewhat straight, the brake system is likely split diagonally, so if you loose pressure on the left front for example, the right rear will have none either, however the right front and left rear would be unaffected. In theory.
Total braking ability and panic stops would be crap though. It's amazing what people drive on through with cars sometimes.
Interesting automotive tidbit: In the 80's Volvo had a version of this setup that split each front four piston caliper into two totally separate hydraulic units for the top two opposing pistons and the bottom two, two brake lines to each wheel. They split it such that if you lost one hose for example on the left front wheel, you'd only loose 50% of the braking ability on that wheel and (again theory) have more controlled braking still. It was also twice the lines and parts to replace. They ran that setup on the 240 for a long while, I think till ABS came along in the early 90's. Rears were normal two piston disks, tied to one of the front circuits on each respective side I think. Been awhile since I had one. Were also an annoyance to bleed. Great brakes on those cars when in good order though, vented disks were a good upgrade.