I would deffinetly NOT deactivate.... most poeple 'get' that they can't get something this close to Christmas, but they may want to buy it, print a picture & give that to the person. It's what we did a LOT at the jewelry store I worked at.... Christmas rings being sized, mother's day rings, etc. I think only a few people were fussy that they couldn;t have the product right away, but most were giddy that they found the 'perfect' gift and not having it on the actual day was secondary.
I WOULD, however, post over and over that all orders will not be sent prior to Christmas, that estimated shipment date is 1/1/2013 (or whatever date). Put it in your announcements, your note to buyer, your about page, even your listings. You might even include a new posting for a custom gift wrapped picture of the product that somebody purchased for a small fee. Say, for $10-15 you will print a nice photograph of the product they bought, put it in a picture frame (Wal-Mart has some nice cheap ones), wrap it with a bow and send it to the recipient.