Automagica would head for World PvP in Hillsbrad. Eye for an Eye would head into the Horde cities for a final extermination. Destructive Reach would do some old-fashioned exploring, both in instances and out, and get contact information for a lot of ingame friends. And Double Bubble, after one last Kara run, would go back to a favorite fishing hole with a favorite pet, and serenely wait for the world to end.
As much as I love instances, I've already run them so much, and I worry that most of my five hours would be taken up with trying to find a group, so I'd probably quest solo (assuming the servers would actually stay up). My Hunter, at 65, would probably too far behind to finish off at 70, so I'd probably do a mad dash for 70 on my Rogue, currently 68. And I'd end the world just as I dinged the highest level on my second 70, which I would consider a proud accomplishment. What would you do with your last five hours in Azeroth?