Is it forbidden to publish old articles that are no longer available on the internet, with the aim of profiting from advertisements, while ensuring that they are free from unlawful content?

The consideration for preserving the copyright is based on the author's permission to publish the article, not on whether it is updated or not. Updating an article does not mean its author has neglected it or become disinclined towards it, to be analogized with material things that their owners abandon due to their disinclination towards them, as stated in the words of Ibn Qudamah and Ibn Taymiyyah. The solution is for the inquirer to edit the articles, such as by summarizing and simplifying, and by adding and modifying.