{"category": "Unity Engine/Editor/Extensions", "keywords": "Unity, Editor, Alert, Message, Remove, Component"} Custom editor to show alert message on remove component.

AlertOnRemoveComponentEditor.cs

using System;
using System.Reflection;
using UnityEditor;
using UnityEngine;

// [CustomEditor(typeof(YOUR_COMPONENT))]
public class AlertOnRemoveComponentEditor :
#if ODIN_INSPECTOR
    Sirenix.OdinInspector.Editor.OdinEditor
#else
    UnityEditor.Editor
#endif
{
    public static string GetAlertMessageOnRemoveMethodName { get; set; } = "GetAlertMessageOnRemove";
    public bool AlertInPlayMode { get; set; } = false;
    public string AlertMessageOnRemove { get; set; }
    

#if ODIN_INSPECTOR
    protected override void OnEnable()
    {
        base.OnEnable();
#else
    protected virtual void OnEnable()
    {
#endif
        if (AlertInPlayMode || !Application.isPlaying)
        {
            InitializeAlertMessageOnRemoveFromTarget();
        }
    }

#if ODIN_INSPECTOR
    protected override void OnDisable()
    {
        base.OnDisable();
#else
    protected virtual void OnDisable()
    {
#endif
        if (AlertInPlayMode || !Application.isPlaying)
        {
            AlertComponentRemoved();
        }
    }

    protected void InitializeAlertMessageOnRemoveFromTarget(string defaultMessage = null)
    {
        Type targetType = target.GetType();
        MethodInfo miGetAlert = null;
        Type hierarchyType = targetType;
        while (hierarchyType != null && miGetAlert == null)
        {
            miGetAlert = hierarchyType.GetMethod(GetAlertMessageOnRemoveMethodName,
                BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Static);
            hierarchyType = hierarchyType.BaseType;
        }

        if (miGetAlert != null)
        {
            if (miGetAlert.IsStatic)
            {
                AlertMessageOnRemove = miGetAlert.Invoke(null, null) as string;
            }
            else
            {
                AlertMessageOnRemove = miGetAlert.Invoke(target, null) as string;
            }
        }

        if (string.IsNullOrEmpty(AlertMessageOnRemove))
        {
            AlertMessageOnRemove = !string.IsNullOrEmpty(defaultMessage)
                ? defaultMessage
                : $"You removed the '{targetType!.Name}' component.";
        }
    }

    protected void AlertComponentRemoved()
    {
        if (!target && EditorUtility.DisplayDialog("Alert", AlertMessageOnRemove, "Revert", "Ignore"))
        {
            Undo.PerformUndo();
        }
    }
}