This subject comes up occasionally, and I'm just going to re-iterate what has been said before... We will not be deleting old diaries unless the author specifically asks us. The aim of DearDiary when it was originally started still holds true and that is to chronicle the passage of time through the eyes of ordinary people so that in 25/50/100 years people can look back and see what REAL people thought about situations, not what the history books say. What good would deleting old, non recently used diaries do for that cause? :)
No, we have plenty of space on the new server, and hard disk drives grow in capacity FAR faster than diary writers can hope to keep up with, so its not likely to ever be an issue :)
No-one's diary will be deleted, unless they specifically ask for it.