unsub-github.user.js

// ==UserScript==
// @name         Github Unsubscribe
// @namespace    http://tampermonkey.net/
// @version      0.3
// @description  Unsubscribe merged or closed threads!
// @author       You
// @match        https://github.com/notifications
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

    let reload = false;
    document.querySelectorAll('.list-group-item.unread').forEach(item => {
        if (item.querySelector('.type-icon-state-closed, .type-icon-state-merged')) {
            reload = true;
            item.querySelector('.btn-link.mute-note').click();
        }
    })
    if (reload) {
        location.reload()
    }
})();