It is still an active service that allows you to play Black Ops 2 multiplayer online. However, if you are referring to the Xbox 360 servers being shut down, it is possible that online multiplayer for Black Ops 2 on Xbox 360 may no longer be available.
If you're having trouble connecting to the Call of Duty: Modern Warfare, you should first check Call of Duty: Modern Warfare Server Status. If the status indicator for your platform is not green or an alert is present, you might encounter connectivity issues until service is restored and fully operational.