When you delete a product that is discontinued or if a product is not currently available, the photo and link to it as a Related Product disappears on the product page it was linked to. Is there a way to check if a product that has become unavailable or discontinued is being used as a Related Product prior to deleting it? If so we we can take note and add another related product to any of the product pages that will be affected. We don't currently use Up-Sells or Cross-Sells but I would assume there is the same issue with them. I can't find info on this but it seems like this is something every store is going to run into. Any help would be much appreciated!
I think an alternative in your scenario could be setting Magento to display out-of-stock products, and then set the visibility for that product to be "visible in catalog", and uncheck all the categories for the product.
As a result, your product won't be included in search results, and it won't be accessible from the catalog since it hasn't been included in any category. It's good to mention that the product will be displayed in search results in Google.
By doing that, the product will be visible from the related products block, but it won't be accessible from the categories or search results.