Redirecting pages is not difficult if you have our Yoast SEO Premium plugin, which can help you to take care of redirects. Preferably, you redirect the old URL (301) to the page or product that replaced the old page or product, or a related page if there is no replacement. That could be the category page of the specific product, or, as a very last resort, your homepage. This way the (outdated) page won’t interfere with your site structure anymore.