Pros and cons of closing topics after they've been long answered?

Good point @DannyPancratz  My view is not to close these topics because, as you say, there are still more clarifying comments related to the original post.
All topics would still be indexed in search regardless of being closed or open I assume - would a closed older post with a higher keyword count of the search term come up before a more recent open one with less keyword count? If yes, that’s not a great UE.
It’s a case by case situation where new topics would need to be raised.
Thirdly, having the system default of displaying old comments first IMO doesn’t help with these long old topics. Switching it to newest first would make the thread easier to follow. Even in this community, I find myself instantly switching to newest first when I can see there’s a lot of comments,  There is an open idea here related to this one. 

Thanks @DannyPancratz for the conversational starter.

My point of view would be it is OK to keep the topic open as long as the original post is still relevant.

i.e. unless the original topic becomes obsolete, or is no longer relatable to the current state of the product or practice, then I would keep the option open to reply and converse.

If the original post does nothing but confuse users due to out of date info, then I would take action.

1. Create an updated topic
2. Link to new topic in a reply
3. Close old out of date topic.

If you encounter a situation where the reply could. be its own topic, then from control we can move it to a NEW topic and start a new conversation there.

As mentioned by @sarahmasterton-brown the fact a topic is closed or not will not be considered in search result ranking.

The sorting oldest to newest helps follow the conversation, but for long conversations is does add a little effort to get the latest and greatest.

@sarahmasterton-brown & @Alistair FIeld good points. Thanks for your input. 

I appreciate the feedback as well. I’m just about to start a community clean up. 

I’m considering making an Archive of old unanswered topics and moving topics that are somewhere between 3-6 months old with no replies there. Before I do that, I’d post in the community, saying what I was going to do - and ask people to bump their topics old topics, if they still need an answer. Anything not bumped (IE commented on) would be moved to hidden archive. 

I would keep it visible to employee, so that if they have time, they could go through and answer topics that need a reply. But mostly, I want employees to spend their time on the new ones that come in. I doubt that anyone with a 6 month old question is still waiting on a reply.