Wiget with dropdown and back compatibility

widget.php

<?php

add_action( 'widgets_init',  'register_my_scheduled_posts_widget' );

function register_my_scheduled_posts_widget() {
	register_widget( 'My_Scheduled_Posts_Widget' );
}

class My_Scheduled_Posts_Widget extends WP_Widget {

	public function __construct() {
		$widget_ops = array(
			'classname' => 'scheduled_recent_entries',
			'description' => __( 'Your site&#8217;s most recent (scheduled) Posts.' ),
			'customize_selective_refresh' => true,
		);
		parent::__construct( 'scheduled-recent-posts', __( 'Scheduled Posts' ), $widget_ops );
	}

	/**
	 * Get validated widget instance settings with back compatibility.
	 */
	function get_instance_settings( $instance ) {
		/*
		 * Check if the old checkbox 'status_future' setting exists.
		 * And if the new dropdown 'include_posts' setting doesn't exist.
		 */
		if ( isset( $instance['status_future'] ) && ! isset( $instance['include_posts'] ) ) {

			// Back compatibility!
			// Update the dropdown 'include_posts' setting with the old checkbox 'status_future' setting if it was set.
			$instance['include_posts'] = $instance['status_future'] ? 'future' : 'all';
		}

		// Check if the dropdown 'include_posts' setting exists and has a value.
		if ( ! ( isset( $instance['include_posts'] ) && $instance['include_posts'] ) ) {
			// Set it to default 'all'
			$instance['include_posts'] = 'all';
		}

		return $instance;
	}

	/**
	 * Widget display.
	 */
	public function widget( $args, $instance ) {
		// Get validated instance settings with back compatibility.
		$instance = $this->get_instance_settings( $instance );

		$include = (string) $instance['include_posts'];

		/*  ***** Query for posts and display them here *****  */
	}

	/**
	 * Update widget settings.
	 */
	public function update( $new_instance, $old_instance ) {
		$instance = $old_instance;

		$instance['include_posts'] = $new_instance['include_posts'];

		// Back compatibility!
		// Don't update (checkbox) 'status_future' setting ever again.
		unset( $instance['status_future'] );

		return $instance;
	}

	/**
	 * Widget settings form.
	 */
	public function form( $instance ) {
		// Get validated instance settings with back compatibility.
		$instance = $this->get_instance_settings( $instance );
		$include  = $instance['include_posts'];

		// Dropdown options
		$include_options = array(
			'all'    => __( 'all posts', 'your-plugin-textdomain' ),
			'future' => __( 'posts with future dates only', 'your-plugin-textdomain' ),
			'year'   => __( 'posts from the current year', 'your-plugin-textdomain' ),
			'month'  => __( 'posts from the current month', 'your-plugin-textdomain' ),
			'day'    => __( 'posts from today', 'your-plugin-textdomain' ),
		);

?>
<p>
	<label for="<?php echo $this->get_field_id( 'include' ); ?>">
		<?php _e( 'Include Posts:', 'your-plugin-textdomain' ); ?>
	</label>
	<select name="<?php echo $this->get_field_name( 'include' ); ?>" id="<?php echo $this->get_field_id( 'include' ); ?>" class="widefat">
		<?php foreach ( $include_options as $name => $label ) : ?>
		<option value="<?php echo esc_attr( $name ); ?>" <?php selected( $include, $name ); ?>>
			<?php echo $label; ?>
		</option>
		<?php endforeach; ?>
	</select>
</p>
<?php
	}
}