Hi Thierry,
What Asad has said is incorrect. There is no end date in the blog nor have I ever seen one in any blog. You can delete a post if you want but its a very unusual use case.
When you create web pages they "should" generally be permament. They get indexed by google and other search indexes and its not good if later they become 404 page not found errors when people click the search results. Its bad for your page rank and search engine optimization.
No-one has ever asked me to implement an end date for blog posts. Its not a common scenario to want to do that.
Hope it helps,
Joe