Brake rotors last much longer than pads, but they are still a wear item with a finite life. How long yours last depends on driving, climate, and pad choice. Here is a realistic picture of rotor lifespan.
Typical rotor life
Rotors commonly last anywhere from about 30,000 to 70,000 miles, and often much more - frequently outlasting one or two sets of pads. Unlike pads, which wear on a predictable schedule, rotor life varies widely with conditions. Many rotors are replaced not because they are worn thin but because of warping or rust.
What shortens rotor life
Hard or heavy braking, towing, mountain driving, and lots of stop-and-go wear rotors faster through heat and friction. Aggressive semi-metallic pads wear rotors quicker than ceramics. In the salt belt, corrosion often kills rotors before wear does - see how to prevent rotor rust. Riding the brakes and repeated overheating cause warping.
When to replace regardless of miles
Replace a rotor when it reaches its minimum thickness - see rotor minimum thickness - or when it warps and causes a pulsation, is deeply scored, cracked, or badly rusted/pitted; see when to replace rotors. Any of these ends a rotor's life early, regardless of mileage.
Getting the most life
Bed pads and rotors properly, avoid riding the brakes, use appropriate pads, and keep the car driven so rotors do not rust from sitting. When rotors are due, replace as a pair with quality pads and fresh hardware, and compare how long pads last.