Hi,
Yes and no.
If you try to load a cart with a product which isn't available anymore, the cart will automatically remove the product from the cart and display a message to the customer that the product is not available. So it should not possible to finish a checkout with a cart containing a product that isn't available.
However, once the order is created it means that the order is valid and then the product settings (quantity, availability, access, etc) are not checked anymore for the order.
If you don't want orders created to be paid outside of the checkout, you can turn off the "Payment of orders not paid immediately" setting of the HikaShop configuration.
And if you keep that setting activated, you can also configure the "order auto cancel" plugin to cancel created orders after a while so that customers can only pay orders during a certain time frame.