Master cylinder failing typically results in loss of all brakes unless you pump them up. Then you could "possibly" limp it to be repaired. This is very dangerous though.
When a wheel cylinder goes bad, it usually leaks. My belief is it still works, however a seal had ruptured and the brake fluid on the brake shoes etc will cause slippage.
A caliper failure would usually be in the form of the piston not returning. Meaning when you step on the brake pedal, the fluid is pushed into a chamber and that pushes a piston which in turn causes the brake pads to be squeezed together. When you release the pedal the fluid is returned to the master cylinder and brake lines, the piston is pushed back in a little. The piston is prone to rust and dirt, and will become stuck in the squeezing position. This is known as a stuck or hung caliper.
00 Regal GS: All kinds of cool stuff.