Topics not replied to in over 30 days (or whatever I decide) will be archived. In other words, if a topic is active it will not be archived.
I personally think that archiving the topics which haven't been replied to in two months will be better. Otherwise you'll get casual users coming on and thinking that they've missed a lot last month because this month seems empty and start shifting through the archives. I don't think anyone would want to shift through any more than two months of topics anways.
So yeah, I vote those older than 2 months to be archived.
Will archives be searchable??? Is there any way to make topics in the achieves replyable??? Will archiving be automated or will it need to be manually initiated???
You can always link to the archive topic in a completely new post. You could also start each subject with "Revisited:" or "Archived:" so that peeple would know its an old topic.