Automatically delete products when stock hits zero, but only after the order is completed.

auto-delete-out-of-stock-products.php

add_action( 'woocommerce_order_status_completed', function( $order_id ) {
    $order = wc_get_order( $order_id );

    if ( ! $order ) {
        return;
    }

    foreach ( $order->get_items() as $item ) {
        $product = $item->get_product();

        if (
            $product instanceof WC_Product &&
            $product->managing_stock() &&
            $product->get_stock_quantity() <= 0
        ) {
            wp_delete_post( $product->get_id(), true );
        }
    }
});