This will migrate sites from a multisite into the main blog.

migrate-multisite-to-mainsite.php

<?php
/*********************************
||||        MAGIC.SCRIPT      ||||
||||            XX            ||||
||||     -----------------    ||||
||||     for migrating        ||||
||||     multisite posts      ||||
||||     into a single site   ||||
 **********************************/
 
 /*
 * For my purposes this file needed to reside outside 
 * of the wp-content directory.  I didn't import everything
 * at once because I like to keep an eye on things to avert
 * potential disasters.
 */


require('wp-blog-header.php');

	global $wpdb;
	$args = array(
		'network_id' => $wpdb->siteid,
		'public'     => null,
		'archived'   => null,
		'mature'     => null,
		'spam'       => 0,
		'deleted'    => null,
		'limit'      => 100,
		'offset'     => 0,
	);


	$my_sites = wp_get_sites( $args );

foreach( $my_sites as $my_site ) {
	$tc_blog_id = $my_site['blog_id'];

	switch_to_blog( $tc_blog_id );
	echo '<h2>The current blog id is ' . get_current_blog_id() . '</h2>';

	$posts = get_posts(
		array(
			'posts_per_page' =>  500,
			'post_status'    => 'publish',
			'post_type'      => 'post'
		)
	);
	echo '<h3>There are ' . count( $posts ) . ' posts in this blog.</h3>';
	//var_dump( $posts );

	restore_current_blog();

	foreach ( $posts as $post ) {
		//echo '<p>' . $post->post_title . ' ' . '-- ' . $post->post_author . '</p>';
		$args = array(
			'post_title'        => $post->post_title,
			'post_content'      => $post->post_content,
			'post_author'       => $post->post_author,
			'post_date'         => $post->post_date,
			'post_date_gmt'     => $post->post_date_gmt,
			'post_name'         => $post->post_name,
			'post_status'       => $post->post_status,
			'ping_status'       => $post->post_status,
			'to_ping'           => $post->to_ping,
			'pinged'            => $post->pinged,
			'post_modified'     => $post->post_modified,
			'post_modified_gmt' => $post->post_modified_gmt,
			'post_parent'       => $post->post_parent,
			'guid'              => $post->guid,
			'post_type'         => $post->post_type,
			'post_mime_type'    => $post->post_mime_type,
			'comment_count'     => $post->comment_count,
		);
		wp_insert_post( $args );
	}
}
wp_cache_flush();

//var_dump($my_sites);