scratch_3.php

<?php
add_filter( 'woocommerce_return_to_shop_redirect', function ( $shop_url ) {
	if ( is_cart() && wc()->cart->cart_contents_count == 0 ) {
		$deleted_items = wc()->cart->get_removed_cart_contents();
		$deleted_items = array_reverse( $deleted_items );
		foreach ( $deleted_items as $deleted_item ) {
			$deleted_id = (int) $deleted_item['product_id'];
			$vendor_id  = wcfm_get_vendor_id_by_post( $deleted_id );
			if ( $vendor_id ) {
				return wcfmmp_get_store_url( $vendor_id );
			}
		}
	}

	return $shop_url;
} );