A car can be driven with bad brake rotors but it's not safe to do so.
The brake rotors are a very important part of your vehicles brake system and without the brake rotors your vehicle will not be able to stop.
Your brake rotors could eventually break apart when driving down the road and stopping as I've seen it happen at least once before.
If you notice cracks in the brake rotor, warps or the rotor is getting thin you really should change them out with new ones.
It's not worth the risk of not being able to stop the vehicle and crashing the vehicle and possibly getting injured or killed.
If you do have bad brake rotors go get them replaced as soon as possible before they cause a bad wreck.