Susan,
Sorry to hear that you missed the Haunted Mansion on your last visit. Sometimes Disney needs to close rides for cleaning, repair, and/or major updates. Although inconvenient at times, I think it is part of what keep WDW so special for everyone.
As you are probably aware, WDW recently started including rehab/closing information on their web site (click
here to see the site). As you are also likely aware, it currently only lists information out through October 2008. I am not 100% sure, but it appears that their list is updated with the same timing of the park calendar, which means that they would publish rehabs/closings for November at the beginning of May (approximately 6 months in advance).
There are other sources on the internet that might be able to help you plan a little farther into the future. A few top-of-mind options include:
www.allearsnet.com (search for "rehabs")
www.wdwinfo.com (select "Theme Parks" from the home page, and then select "Rehabs/closings")
www.intercot.com (select "rehabs/closings" from the list on the left of the home page)
Fortunately
none of these sources indicate a planned closure/rehab for the Haunted Mansion.
Have a great visit in November, and say "Hi" to those 999 grinning ghosts for me - OK?