Event Aggregator - delete events before import

delete-events-before-import.php

<?php
/**
 * Created by PhpStorm.
 * Plugin Name: Berean Baptist Church Calendar Import Fixer
 * Description: Forces removal of events no longer represented in the imported calendar.
 * Version: 0.0.1
 * Author: Steve Dwire for Berean Baptist Church
 * Author URI: https://www.berean-baptist.org/
 * License: GPLv2
 */

class BBC_EC_ImportFixer {
    const VERSION = '0.0.1';

    public function __construct() {
        add_action( 'init', array( $this, 'init' ) );
    }

    public function init() {
        add_action( 'tribe_aggregator_record_finalized', array( $this, 'handle_before_insert_posts'), 10, 2 );
    }

    public function handle_before_insert_posts($record_id, $record_meta ) {
        $this_category_term_id = Tribe__Utils__Array::get( $record_meta, 'category', false );

        if ( empty( $this_category_term_id ) ) {
            return;
        }

        $relevant_existing_events = tribe_get_events( [
            'fields'     => 'ids',
            'start_date' => date( 'Y-m-d H:i:s', time() ), // starting now or later
            'tax_query'  => [
                [
                    'taxonomy' => Tribe__Events__Main::TAXONOMY,
                    'field'    => 'term_id',
                    'terms'    => [ $this_category_term_id ],
                    'operator' => 'IN'
                ]
            ],
            'meta_key' => '_uid',
            'meta_value' => $record_meta['ids_to_import'],
            'meta_compare' => 'NOT IN'
        ] );

        foreach ( $relevant_existing_events as $event_id ) {
            wp_delete_post( $event_id, true );
        }

    }
}

new BBC_EC_ImportFixer();

Hi @joeykb
Sorry, only saw your comment now.
Create an empty file in your wp-content/plugins folder, like wp-content/plugins/import-fixer.php
Then copy the full contents which you see above in that file. Save it.
In your admin go to Plugins and activate the "Berean Baptist Church Calendar Import Fixer" plugin.
That should be it.
Note, I think it only works for events that have a category. If you want to use this for any and all events, then delete lines 24-28. Also note, I haven't tested this part. :)

Note that $this_category_term_id is used in the query for "terms" and removing that would likely cause an error. Also, this will delete all events that are not in the current import. This may not be desired if you have more than one import source.