Find out if a user has published content on a multisite WordPress install.

rt_user_has_published_content.php

/**
 * Find out if a user has published content anywhere on the (multi-)site
 */
function rt_user_has_published_content( $user_id ) {
	// Arguments for get_posts, requesting 1 post of any type.
	$args = array(
		'post_type' => 'any',
		'posts_per_page' => 1,
		'author' => $user_id,
		'fields' => 'ids',
	);
	// Distinguish between multisite and single site.
	if( is_multisite() ){
		// Get all subsites where the user has a role.
		$user_subsites = get_blogs_of_user( $user_id );
		// Return false if the user does not have any roles at all.
		if( empty( $user_subsites ) ){
			return false;
		}
		// Loop through the subsites to check for content, return true is any is found.
		foreach( $user_subsites as $key => $subsite ){
			$post_count = 0;
			switch_to_blog( $key );
			$user_posts = get_posts( $args );
			$post_count = count( $user_posts );
			restore_current_blog();
			if( $post_count > 0 ){
				return true;
			}
		}
		// No content found.
		return false;
	} else {
		$user_posts = get_posts( $args );
		$post_count = count( $user_posts );
		if( $post_count > 0 ){
			return true;
		}
		return false;
	}
}