@AndyB - there is a bug. If thread starter is deleted from forum, than anybody can post into deleted thread starter's thread , no just Staff and thread starter.
There is a bug because thread starter after deleted from forum is guest
One question: It seems the reply button is not hidden if the thread starter doesn't refresh the page, is there a way to prevent that, to hide the reply button automatically?
All I have to do is set permissions in my staff user groups, instead of setting permissions in every forum like with the other one that I linked in the sentence above.