wpmu_delete_blog

function wpmu_delete_blog( $blog_id, $drop = false ) {
	global $wpdb;

	$switch = false;
	if ( get_current_blog_id() != $blog_id ) {
		$switch = true;
		switch_to_blog( $blog_id );
	}

	$blog = get_site( $blog_id );

	$current_network = get_network();

	// If a full blog object is not available, do not destroy anything.
	if ( $drop && ! $blog ) {
		$drop = false;
	}

	// Don't destroy the initial, main, or root blog.
	if ( $drop && ( 1 == $blog_id || is_main_site( $blog_id ) || ( $blog->path == $current_network->path && $blog->domain == $current_network->domain ) ) ) {
		$drop = false;
	}

	$upload_path = trim( get_option( 'upload_path' ) );

	// If ms_files_rewriting is enabled and upload_path is empty, wp_upload_dir is not reliable.
	if ( $drop && get_site_option( 'ms_files_rewriting' ) && empty( $upload_path ) ) {
		$drop = false;
	}

	if ( $drop ) {
		wp_delete_site( $blog_id );
	} else {
		/** This action is documented in wp-includes/ms-blogs.php */
		do_action_deprecated( 'delete_blog', array( $blog_id, false ), '5.1.0' );

		$users = get_users(
			array(
				'blog_id' => $blog_id,
				'fields'  => 'ids',
			)
		);

		// Remove users from this blog.
		if ( ! empty( $users ) ) {
			foreach ( $users as $user_id ) {
				remove_user_from_blog( $user_id, $blog_id );
			}
		}

		update_blog_status( $blog_id, 'deleted', 1 );

		/** This action is documented in wp-includes/ms-blogs.php */
		do_action_deprecated( 'deleted_blog', array( $blog_id, false ), '5.1.0' );
	}

	if ( $switch ) {
		restore_current_blog();
	}
}