I admit I don't know how reasonable it is to order an authenticator from the US store for players in Europe, so hopefully the store won't be down for long. It should be noted that Takralus specifically points out that physical products will be unavailable, so presumably you can still buy items like pets and mounts.
Mists of Pandaria is here! The level cap has been raised to 90, many players have returned to Azeroth, and pet battles are taking the world by storm. Keep an eye out for all of the latest news, and check out our comprehensive guide to Mists of Pandaria for everything you'll ever need to know.