If you mark a Web Group as No or you delete (obsolete) a web group, the products contained within the web group should no longer show in search results.
You should be able to navigate direct to the product (unless of course the webcatalog says other wise) in case the product is cached / bookmarked.
but the product should not show up in searches, as this maybe a group you are preparing for a launch, or it is something you dont want to promote at this time.
Other wise you need to removed the products from the groups themselves which is a long task.
