I'd like to suggest that old conversations/threads should only be closed when the original poster marks their question/topic as resolved and not after 28 days. To me, this seems like 28 days expiration is just a way for the dev team to feel like they're taking care of things when really they've just let issues people create "expire" instead of actually taking them into consideration and fixing them.
I've come across numerous topics that never actually solve the problem at hand, as well as situations where a new version invalidates the original answer and I'll like to comment such for future readers.
Take a look at how stack overflow does things, they allow linking topics together and never even close a question even after they have been marked as answered. Just because a conversation is old, doesn't mean that it is no longer relevant.