xNode/Scripts/Editor/NodeEditorAssetModProcessor.cs

using System.Collections;
using System.Collections.Generic;
using UnityEditor;
using UnityEngine;

public class NodeEditorAssetModProcessor : UnityEditor.AssetModificationProcessor {
    public static AssetDeleteResult OnWillDeleteAsset(string path, RemoveAssetOptions options) {
        UnityEngine.Object obj = AssetDatabase.LoadAssetAtPath<UnityEngine.Object>(path);

        if (!(obj is UnityEditor.MonoScript)) return AssetDeleteResult.DidNotDelete;

        UnityEditor.MonoScript script = obj as UnityEditor.MonoScript;
        System.Type scriptType = script.GetClass();

        if (scriptType != typeof(Node) && !scriptType.IsSubclassOf(typeof(Node))) return AssetDeleteResult.DidNotDelete;

        //Find ScriptableObjects using this script
        string[] guids = AssetDatabase.FindAssets("t:" + scriptType);
        for (int i = 0; i < guids.Length; i++) {
            string assetpath = AssetDatabase.GUIDToAssetPath(guids[i]);
            Object[] objs = AssetDatabase.LoadAllAssetRepresentationsAtPath(assetpath);
            for (int k = 0; k < objs.Length; k++) {
                Node node = objs[k] as Node;
                if (node.GetType() == scriptType) {
                    if (node != null && node.graph != null) {
                        Debug.LogWarning(node.name + " of " + node.graph + " depended on deleted script and has been removed automatically.", node.graph);
                        node.graph.RemoveNode(node);
                    }
                }
            }

        }
        return AssetDeleteResult.DidNotDelete;
    }
}