The owner of the LFG thread which means the owner of the campaign can delete the those threads that they feel are not applicable anymore. I do not know of any automated way of handling this except for the posters to edit their own threads. It is up in the hands of the campaign owner to do whatever they feel is best for them, you have full moderating power on your own campaigns. A good way to handle this is to make people post in a single thread instead of making new threads each time they apply, that way you can easily delete or post mid-term reports on who gets in and who does not. I myself use this and is very useful, just warn players beforehand that you will ignore/delete any posts not done on the application thread.