As far as I know, the authors cannot delete their articles from the database on their own. However, I have never come across any such case when the author decides to delete all of his/her articles which have been approved and published by ISC.
However, a request has to be raised in the forum in the form of a thread duly mentioning the URL's of the articles and perhaps a reason also for proposed deletion of the threads.
In case, the articles are proposed to be re-published after editing/moderating/updating then, the same can be done only after six months of the original date of publication of the threads.
Sometimes, the previously published threads are locked by the editors and the same are not available even for editing for re-publication and a request is required to be raised in the forum section for 'unlocking' the threads.
In case the article has not yet been published and is required to be deleted at draft stage, then also a request has to be raised in the forum section duly citing the URL.
Let us encourage each other in sharing knowledge.