Thread:SW8573/@comment-4674838-20120912221907/@comment-4795804-20120914090526

Well,
 * If there wasn't the option to disable the auto-archiving with the  setting, I would surely prefer 4)+3), so based off the last action of any kind: The "timer could be reset" both by author when he edited the post and users/author when they add a comment.
 * However, as we have the  setting available, the author has much stronger ability to control the enabling/disabling of the comments, so now it isn't so much important, how the time is calculated. I think that both 4)+2) and 4)+3) are good, so it is up to you which one you prefer, or which one is easier for you to implement. BTW, as "not commented posts" is probably a very rare state, even 1) is a good option.