[WooCommerce, WordPress ]This snippets contain get_product_by_slug , and redirect from single product page to somewhere when product is out f stock.

woo_out_of_stock.php

/**
* Retrieve a product given its slug.
*/
function get_product_by_slug($page_slug) {
    global $wpdb;
        $product = $wpdb->get_var( $wpdb->prepare( "SELECT ID FROM $wpdb->posts WHERE post_name = %s AND post_type= %s", $page_slug, 'product'));
        if ( $product )
            return wc_get_product($product);
    return null;
}
/**
* Redirect somewhere from page where product is out of stock
*/
function redirect_out_of_stock_product( $query ) {

	if( !is_admin() && $query->is_main_query() && $query->query['post_type'] === 'product' ){
		$product = get_product_by_slug($query->query['name']);
		if( !$product->is_in_stock() ){
			wp_redirect( 'https://example.com/some/page' );
		}
	}

}
add_action( 'pre_get_posts', 'redirect_out_of_stock_product' );