Archive is just a list of of older posts so it is always possible to find them even when they are no longer in the main page of the post list (usually this happens because they have been pushed off the first page of the list by newer posts.
Most blogs do not have an end date feature because content generally is not supposed to disappear from the internet, but people asked for an end date to use the blog more like a news feature and they wanted the content to be not available after the end date as if the post no longer exists. So that is how it works, it should not be possible for users to see any blog post that has passed its end date. If you want people to be able to always get to older posts just don't use an end date. It is not an "archive date" it is an end date.
Hope that helps,