Call Microthemer custom CSS file from functions so the plugin can be turned off or uninstalled.
From https://themeover.com/forum/topic/microthemer-customizations-when-deactived/
/* Begin Microthemer Code */
function add_microthemer_css() {
if (!defined('MT_IS_ACTIVE')) {
$p = get_option('preferences_themer_loader');
if (!empty($p['g_fonts_used'])){
$p['g_url'] = !empty($p['gfont_subset']) ? $p['g_url'] . $p['gfont_subset'] : $p['g_url'];
wp_register_style( 'microthemer_g_font', $p['g_url'], false );
wp_enqueue_style( 'microthemer_g_font' );
}
wp_register_style( 'microthemer', content_url() . '/micro-themes/active-styles.css');
wp_enqueue_style('microthemer');
}
}
add_action('wp_enqueue_scripts', 'add_microthemer_css');
/* End Microthemer Code */