Scott Nelle

WordPress lets you set a number of days after which comments will be unavailable for individual posts. This plugin will allow you to keep commenting open on specific posts.
Once the plugin is enabled:
<ul>
<li>Set a comment deadline in Settings > Discussion using the “Automatically Close Comments…” option. Closing comments on old posts is a great way to avoid spam comments.</li>
<li>Edit an individual post on which you’d like to keep discussion open indefinitely and check the Override Comment Deadline box.</li>
</ul>

Override Comment Deadline

Allows you to enable comments on posts which are older than the comment deadline set in discussion settings.

replyPUSH

Much like WordPress.com’s “Comment Reply via Email”, you can reply to any post you subscribe to.
Integrates with the wonderful <a href="https://wordpress.org/plugins/subscribe2/" title="subscribe2" rel="ugc">subscribe2</a> and <a href="http://replypush.com" title="replyPUSH.com" rel="nofollow ugc">replyPUSH.com</a> service to provide the email reply magic.
It automatically adds notifications for comment posts to keep the conversation flowing 🙂
All the subscriber need do, is reply at the top of their quoted email notification.

Reply By Email

Allows your users to reply to articles / blog posts and comments via email.

Override Comment Deadline vs Reply By Email