simply by deleting user from the users table will leave all user's content put, which is why we recommend you to find the query in the code which is responsible for deleting user from Admin panel and use it in your SQL statement this way you'll be able to delete a user and his/her content.
The difficult part is that dont think that the delete from admin actually removes the news feed data, i maybe be wrong but i do think there is actually orpan info left there when the user is deleted. Actually think it would be difficult to remove the news feed data this way as the data is somewhat complicated. The only way i know to delete it (if this is the case and its not del by the admin removal of a member) is to go page by page in the main and delete each one at a time manually. (lets hope i am wrong on this)
You could flush the newsfeed table but IMO your opening a real can of woms doing that.
The best way to know for sure is to create a temporary member, post some data, then delete them. Then export your database, and open it up in programmers notepad and do a search for the member name or or nickname or some of the data they posted. I think you will be suprised by how much data is still there.