Hi,
There is no option in order to let the user decide what to do. That's something we want to add in the future.
When you set that "registration" option to "no registration", it removes the username/name/password fields of the registration form and no user is added to joomla. That's the goal of that option. It still asks for the email address and the address of the user. If you want to change the address fields of that form, you can configure them via the menu Display->Custom fields.
And if you don't want that login or registration view, you can remove it from the "checkout workflow" option of the configuration. However, that means that, from a hikashop's point of view, you won't know who ordered your products.