Users have apparently been informed via email that after March 15, they will need to join Skype  to chat with friends on Messenger. Buddy lists will automatically be migrated, saving users the hassle of re-adding contacts. Users will receive a banner notification to install Skype, which will also uninstall Messenger.
Messenger will continue to live on only in mainland China.
[Image: San Diego Air & Space Museum Archives  on Flickr]