Trouble with Keyword-Rich SEO URL

Is the only problem that the true "page does not exist" URLs are throwing the 500 error? That might well be because you need to set the path to the "Page Not Found" page from the web root on down. So, if you have 404-TBL.html in your web root, you would enter /404-TBL.html into that field.

Here is the scenario.

I add a water filter "A" to my cart.

I add a water filter "B" to my cart.

I set up a cross sell relationship so that "B" shows up on "A" product page.

Works great.

Now I run out of "B" filters, so I go in and make the product inactive because I may not carry it anymore.

Somehow, Google is still seeing the link for product B because the relationship still exists, and when you click on product "B" it lets you try to buy it even though it is marked inactive in the control panel.  But then you get a message that says something like "sorry you loser, this product doesn't exist" something to that effect.

We were getting dinged by Google for this in a pretty major way.

It would be really cool if ProductCart had a "remove all inactive products from relationships" script or automatically removed relationships when a product is marked as inactive.

Any thoughts or comments are welcome.