Allows you to add a search a Unity project for all instances of missing mono script.

FindMissingScripts.cs

using UnityEngine;
using UnityEditor;
public class FindMissingScripts : EditorWindow {
 
    [MenuItem("Window/FindMissingScripts")]
    public static void ShowWindow()
    {
        EditorWindow.GetWindow(typeof(FindMissingScripts));
    }
 
    public void OnGUI()
    {
        if (GUILayout.Button("Find Missing Scripts in selected prefabs"))
        {
            FindInSelected();
        }
    }
    private static void FindInSelected()
    {
        GameObject[] go = Selection.gameObjects;
        int go_count = 0, components_count = 0, missing_count = 0;
        foreach (GameObject g in go)
        {
            go_count++;
            Component[] components = g.GetComponents<Component>();
            for (int i = 0; i < components.Length; i++)
            {
                components_count++;
                if (components[i] == null)
                {
                    missing_count++;
                    Debug.Log(g.name + " has an empty script attached in position: " + i, g);
                }
            }
        }
 
        Debug.Log(string.Format("Searched {0} GameObjects, {1} components, found {2} missing", go_count, components_count, missing_count));
    }
}

FindMissingScriptsRecursively.cs

using UnityEngine;
using UnityEditor;
public class FindMissingScriptsRecursively : EditorWindow {
static int go_count = 0, components_count = 0, missing_count = 0;
 
    [MenuItem("Window/FindMissingScriptsRecursively")]
    public static void ShowWindow()
    {
        EditorWindow.GetWindow(typeof(FindMissingScriptsRecursively));
    }
 
    public void OnGUI()
    {
        if (GUILayout.Button("Find Missing Scripts in selected GameObjects"))
        {
            FindInSelected();
        }
    }
    private static void FindInSelected()
    {
        GameObject[] go = Selection.gameObjects;
        go_count = 0;
		components_count = 0;
		missing_count = 0;
        foreach (GameObject g in go)
        {
   			FindInGO(g);
        }
        Debug.Log(string.Format("Searched {0} GameObjects, {1} components, found {2} missing", go_count, components_count, missing_count));
    }
 
    private static void FindInGO(GameObject g)
    {
        go_count++;
        Component[] components = g.GetComponents<Component>();
        for (int i = 0; i < components.Length; i++)
        {
        components_count++;
        if (components[i] == null)
            {
            missing_count++;
            Debug.Log(g.name + " has an empty script attached in position: " + i, g);
            }
        }
        // Now recurse through each child GO (if there are any):
        foreach (Transform childT in g.transform)
            {
            //Debug.Log("Searching " + childT.name  + " " );
            FindInGO(childT.gameObject);
            }
	}
}