Hi,
If the login form was removed too, please check that the "login" setting is activated under the checkout tab of the hikaShop configuration, and that you have the "login" view added in the "checkout workflow" setting there.
Regarding the registration form, it's normal that it will be removed if you turn off the registration on your website. If you want a form without registration, you would have to set the "registration" setting to "guest" in the "checkout" tab of the HikaShop configuration. That will allow your customers to checkout without registration/login, as guests.