Implemented an option to call widget initialization on demand (for PJAX, AJAX or other purposes).

TinyMce.php

<?php
/**
 * @copyright Copyright (c) 2013-2017 2amigOS! Consulting Group LLC
 * @link http://2amigos.us
 * @license http://www.opensource.org/licenses/bsd-license.php New BSD License
 */
namespace dosamigos\tinymce;

use yii\helpers\Html;
use yii\helpers\Json;
use yii\widgets\InputWidget;

/**
 *
 * TinyMCE renders a tinyMCE js plugin for WYSIWYG editing.
 *
 * @author Antonio Ramirez <amigo.cobos@gmail.com>
 * @link http://www.ramirezcobos.com/
 * @link http://www.2amigos.us/
 */
class TinyMce extends InputWidget
{
    /**
     * @var string the language to use. Defaults to null (en).
     */
    public $language;
    /**
     * @var array the options for the TinyMCE JS plugin.
     * Please refer to the TinyMCE JS plugin Web page for possible options.
     * @see http://www.tinymce.com/wiki.php/Configuration
     */
    public $clientOptions = [];
    /**
     * @var bool whether to set the on change event for the editor. This is required to be able to validate data.
     * @see https://github.com/2amigos/yii2-tinymce-widget/issues/7
     */
    public $triggerSaveOnBeforeValidateForm = true;

    /**
     * @inheritdoc
     */
    public function run()
    {
        if ($this->hasModel()) {
            echo Html::activeTextarea($this->model, $this->attribute, $this->options);
        } else {
            echo Html::textarea($this->name, $this->value, $this->options);
        }
        $this->registerClientScript();
    }

    /**
     * Registers tinyMCE js plugin
     */
    protected function registerClientScript()
    {
        $js = [];
        $view = $this->getView();

        TinyMceAsset::register($view);

        $id = $this->options['id'];
        $callback = 'tinymceInit_' . $id;

        $this->clientOptions['selector'] = "#$id";
        // @codeCoverageIgnoreStart
        if ($this->language !== null && $this->language !== 'en') {
            $langFile = "langs/{$this->language}.js";
            $langAssetBundle = TinyMceLangAsset::register($view);
            $langAssetBundle->js[] = $langFile;
            $this->clientOptions['language_url'] = $langAssetBundle->baseUrl . "/{$langFile}";
        }
        // @codeCoverageIgnoreEnd

        $options = Json::encode($this->clientOptions);

        $js[] = 'var options = ' . $options . ';';
        $js[] = 'tinymce.init(options);';
        if ($this->triggerSaveOnBeforeValidateForm) {
            $js[] = "$('#{$id}').parents('form').on('beforeValidate', function() { tinymce.triggerSave(); });";
        }
        $js[] = '$(document).trigger("tinymce:init", ["' . $callback . '", options]);';
        $view->registerJs('var ' . $callback . ' = function() { ' . implode("\n", $js) . '}', $view::POS_END);
        $view->registerJs($callback . '();');
    }
}

Your code could reload all tinyMCEs with code like this:

(function() {
var tinymceCallbacks = [];
$(document).on('tinymce:init', function(e, callback, options) {
    console.log('TinyMCE was initialized with callback', callback);
    if (!$.inArray(callback, tinymceCallbacks)) {
        tinymceCallbacks.push(callback);
    }
});
$(document).on('pjax:complete', function() {
    $.each(tinymceCallbacks, function(callback) {
        callback.call(this);
    });
});
})();