Another idea for resurrected threads is to present them with some indicator in the index page that will alert users that the thread has more than one extended intermission and when the user opens the thread the text is sectioned every time there is an intermission.
For example, thread starts on Jan 15th, has a bunch of posts until April, then users resurrect it in June, October and December, so the when users view the thread there'll be 4 sections separated by some graphic that clearly tells users that one is responding to an extended thread and some of the original posters may or may not be around to respond to you (users that have quit the website, for example, or who have not been around much).
The graphic(s) could be a heavy line, or a slight change in background color, or any other interesting design that clearly separates each set of posts from the more and most recent section(s).