Brake discs or brake rotors and brake pads should last from 30,000 to 70,000 miles.
It's recommended that you replace your brake discs or brake rotors after every other brake pad change.
Same with the brake drums replace those after every other brake shoe change and also change the brake wheel cylinders when changing the brake shoes and brake drums while you have it down.
Wheel cylinders cost less than $10.00 a piece and are worth replacing since you have the brakes torn down.