public class MySuperAwesomeSubclassThatGetsFaded : MonoBehaviour{
    bool shouldFadeOut = true;
}

public class Fader : MonoBehaviour{
    void Start(){
        MySuperAwesomeSubclassThatGetsFaded superAwesomeInstance;
        FadeOut(superAwesomeInstance);
        //later...
        superAwesomeInstance.shouldFadeOut = false; //kill the fade
    }

    IEnumerator FadeObject (MySuperAwesomeSubclassThatGetsFaded subc) {
        while (SomeFadingTest) {
            //  SomeFadingCode()
            if(!subc.shouldFadeOut) return; //if the flag on the object gets set to false, then stop the fade
            yield return null;
        }
    // Put object back in the pool code
    }
}