Google Product Forums
Re: Will 404 Not Found error always occur when I change the inventory and delete products/web pages?
Michael Martinez Oct 20, 2009 9:28 PM
Posted in group: Webmaster Central

Categories: Crawling, indexing & ranking :

It depends on the software you're using for your online store.

As long as there are no surviving links for the deleted URLs you should be okay.  Over time they will indeed fall out of the system.  But you may have to implement 301-redirects for the deleted URLs.