Download Archive of Chat History When a Server is Deleted

I am a person who really likes to keep archives of my personal history, as a sort of alternative to a diary, but I can only have 100 servers. It would be nice if I could download an archive of chat messages when I delete or leave a server so I can refer to them at a later date. I know you can download all of your chat histories but I want to preserve entire servers when I end up deleting them.