functions.php

<?php

function my_find_expired_events( $ids ) {

	$args = array(
		'post_type'     => 'tribe_events',
		'nopaging'      => true,
		'fields'        => 'ids',
		'meta_query'    => array(
			array(
				'key'       => '_EventEndDate',
				'value'     => date( 'Y-m-d H:i:s' ),
				'compare'   => '<',
				'type'      => 'DATETIME',
			),
		),
	);

	$expired_events = get_posts( $args );

	$ids = array_merge( $ids, $expired_events );
	$ids = array_map( 'absint', $ids );
	$ids = array_unique( $ids );

	return $ids;
}

add_filter( 'searchwp_exclude', 'my_find_expired_events' );