I think it depends on the subreddit. E.g. this is archived: https://old.reddit.com/r/Python/comments/hmoabi/ive_designed...

A Reddit thread is automatically archived due to inactivity, forgot the exact duration. So in theory as long as somebody is posting a comment on a thread every few weeks (months?) it never archives unless the mods manually do it. The problem with this is that adding comments to a thread does nothing to make it more visible. Traditional forms bump up all threads as long as they have recent activity, which Reddit doesn’t do.

The closest solution you could probably find would be for the mods to pin the post to the top, but in my experience most people just ignore pinned posts except in very specific cases.