Hi,
I still don't see how that's possible.
The helper file is loaded with the code:
include_once(rtrim(JPATH_ADMINISTRATOR,DS).DS.'components'.DS.'com_hikashop'.DS.'helpers'.DS.'helper.php')
at the beginning of the file.
As you can see, the path 'components'.DS.'com_hikashop'.DS.'helpers'.DS.'helper.php' is searched in the administrator folder of your website thanks to the JPATH_ADMINISTRATOR constant which is a standard Joomla constant for the administrator folder path.
So I don't see why it wouldn't be able to find the helper.
You can try to add that code ( include_once(rtrim(JPATH_ADMINISTRATOR,DS).DS.'components'.DS.'com_hikashop'.DS.'helpers'.DS.'helper.php'); ) just before the line 43, but I don't see why it would change anything.