uninstall.php

<?php
/**
 * Code used when the plugin is removed (not just deactivated but actively deleted by the WordPress Admin).
 *
 * @package WordPress\Plugins\Demo_Quotes_Plugin
 * @subpackage Uninstall
 */

if ( ! current_user_can( 'activate_plugins' ) || ( ! defined( 'ABSPATH' ) || ! defined( 'WP_UNINSTALL_PLUGIN' ) ) ) {
	exit();
}


$options = get_option( 'demo_quotes_plugin_options' );

if ( isset( $options['uninstall']['delete_taxonomy'] ) && 'DELETE' === $options['uninstall']['delete_taxonomy'] ) {
	// Get all terms with our taxonomy & all relationships to these.
	// Delete.
}
if ( isset( $options['uninstall']['delete_posts'] ) && 'DELETE' === $options['uninstall']['delete_posts'] ) {
	// Get all posts with our post_type & all posts where a post with our post_type is the post_parent (revisions).
	// Delete.
}

delete_option( 'demo_quotes_plugin_options' );