// do something every month
    global $wpdb;
$evil_author = THE_ID_OF_THE_AUTHOR_WHOSE_POSTS_YOU_WANNA_BUZZIATE;
$them_posts = $wpdb->get_results("SELECT * FROM $wpdb->posts WHERE AND post_author = $evil_author" AND post_type = "my_post_type"); // Replace my_post_type  by the post type you want

foreach ( $them_posts as $post_die )
{
    wp_delete_post( $post_die->ID, true ); // Bypasses Trash and deletes all the posts
}

<?php
/*
Plugin Name:My Custom Plugin
Description:My Custom Plugin
Version:1.0
*/

register_activation_hook(__FILE__, 'my_activation');

function my_activation() {
    if (! wp_next_scheduled ( 'my_monthly_event' )) {
    wp_schedule_event(time(), 'monthly', 'my_monthly_event');
    }
}

add_action('my_monthly_event', 'do_this_monthly');

function do_this_monthly() {
    // do something every month
    global $wpdb;
$evil_author = THE_ID_OF_THE_AUTHOR_WHOSE_POSTS_YOU_WANNA_BUZZIATE;
$them_posts = $wpdb->get_results("SELECT * FROM $wpdb->posts WHERE AND post_author = $evil_author" AND post_type = "my_post_type"); // Replace my_post_type  by the post type you want

foreach ( $them_posts as $post_die )
{
    wp_delete_post( $post_die->ID, true ); // Bypasses Trash and deletes all the posts
}
}


// cleaning the scheduler on deactivation:

register_deactivation_hook(__FILE__, 'my_deactivation');

function my_deactivation() {
    wp_clear_scheduled_hook('my_monthly_event');
}

?>