What advantage this user would have for deleting post/topic? Even if he/she still keeping points, the post count will decrease and will take more time to upgrade rank.
In my opinion, users who does this things will be only harming themselves.
Imagine a scenario:
Someone do not have much idea what to post. So what he/she will do is... create a topic or comment in a topic with any thing (literally with
safasdfk lsjf lksjaflj lasfj lkasjf al, whatever they can type randomly pressing the keyboard) then delete it. Again they comment or create a topic and delete it. They keep doing it. End of the they will end up lots of points.
Not possible? I do not think so. It's really easy unless the admin will have a log of what we are deleting and updating. I doubt they have.