AjaxThreadDelete

 plugin allows people to completely delete threads, instead of removing/closing them.

Installation
To install the script, add the following code to your MediaWiki:Common.js, Special:Mypage/common.js or to w:Special:Mypage/global.js

JS
There are several configuration options:

CSS
This configuration should go to your MediaWiki:Chat.css (wiki-wide use) or Special:Mypage/chat.css (personal use).

Future updates

 * Deleting original post automatically deletes all of the other posts