In addition to saving the more recently active and more popular (longer) threads, we also have the Reference forum, where we can move shorter threads that people think would be of value to keep. Anyone can nominate a thread to be potentially moved there if they feel it’s a great thread worth saving for the community at large; otherwise, folks can save threads themselves that are of personal value.
Due to some tweaking we’ve done with the servers and some upcoming changes we’ll be making to all the COTH sites, we should be able to maintain an even greater store of threads on the site. We’re already maintaining about three times the number of threads as we did less than two years ago.
It’s only rarely that we’re contacted regarding a thread that’s no longer available, so for those few instances, it probably wouldn’t be a wise investment of time and resources at this point to maintain all “deleted” threads offline in order to retrieve them on a case-by-case basis.
Thanks for the suggestions–brainstorming never hurts!