Hi,
that's a good question, we had the same issue.
It is possible, but your products have to remain published in order not to get the 404 page.
What you can do, is create a new Hikashop Category called "archived" or something and place your products in there. As long as you don't add this category in any product listing, the products will not be visible to visitors of your webshop, but the product will still be accessible if someone clicks on an old link to it from a search engine for example.
The easiest way not to have an add to cart button is to simply set your product quantities to 0, otherwise you could make a view override not to show the button for all products in this category but that is more complicated.
Hope that helps!