With this, you would close Unity using a menu command instead of pressing the "close cross".

AccidentalProjectClosePrevention.cs

using UnityEngine;
using UnityEditor;

// TODO: rename to 'secret quit button' xD
// Maybe just have a "Sure to quit?" window?

[InitializeOnLoad]
public class AccidentalProjectClosePrevention
{
    [MenuItem("Tools/Quit")]
    static void AllowQuit()
    {
        if (UnityEditor.SceneManagement.EditorSceneManager.GetActiveScene().isDirty)
        {
            Debug.Log("save changes first");
            return;
        }

        EditorPrefs.SetBool("sua_quit_allowed", true);
        EditorApplication.Exit(0);
    }

    static bool WantsToQuit()
    {
        Debug.Log("Editor prevented from quitting. Quit by going Tools -> Quit");
        return false;
    }

    static AccidentalProjectClosePrevention()
    {
        EditorApplication.wantsToQuit += WantsToQuit;
        EditorPrefs.SetBool("sua_quit_allowed", false);
    }
}