Posts that are deemed inappropriate, and posts on threads that get removed for being inappropriate, are deleted and removed from your profile. But as mentioned mere inactivity doesn't delete a thread, just close it.
In practice, there seem to be a bit fewer than 1000 posts on most people's profiles; removed posts may still "count" towards the 1000 but not be shown.
Google searches can sometimes turn up old posts more easily than TripAdvisor searches. Put the user name in quotes, e.g. "Texas123_7", for best results.
Edited: 10:18 am, February 12, 2013