How to get the target when doing OnDestroy() for CustomEditor?

Refers to this question's answer and comments, it suggest that one can declare a static variable to cache the object in OnDisable(), and then use it in OnDestroy() if the object is being destroyed(removed).

But this trick can't work, since the target and whatever being cached are all already becoming null.

Code sample is below:

 [CustomEditor(typeof(MyType))]
  public class MyTypeEditor: Editor
  {
      static private MyType sm = null;
      private MyType m = null;

      public void OnEnable()
      {
          // cache the object, working
          m = (MyType)target;
      }

      public void OnDisable()
      {
          // original answer & comment suggest this way
          // but couldn't work, 
          // since when doing `OnDestroy()`, `m` & `target` are all `null`
          sm = m;
      }

      public void OnDestroy()
      {
          if (target == null) // which means that I am destroying the object not closing inspector
          {
              // use `sm` to get the real object and read it's data
              // which cant work
              // originally wants to read the data and do some un-register process, etc.
          }
      }
  }

The question is, I can distinguish between closing inspector and actually destroying the object by checking if (target == null), but, since the object is already destroyed inside OnDestroy(), how do I read its value? Is there any priorer point I can intercept the destroying process?

Thanks.