As you noted correctly, there aren't any such webhook topics for articles (aka blog posts) or pages. Hence, you will not be able to use the webhook method to subscribe to changes.
I suggest you look to scheduled polling against articles API instead. For deleted articles you will need to keep a list of articles on your app backend for comparison otherwise there'd be no way to tell.
Hope this helps!
Those are basically like an audit trail of events that occurred in your store. You can use them for querying historical events such as who changed what and when, who created what and when, who fulfilled order so and so etc.