We do not know yet how long you'll still be able to use Google Talk. Google has been making it clear they want to move forward with Hangouts, which we have no plans to support. For now, you'll still be able to sign in to Google Talk and talk to people using Hangouts, but we have no information about how long this will be possible.
Speaking of deprecated services, we believe MSN is now totally dead. We expect this to be permanent, we currently have no plans to support Skype.
Facebook Chat will also stop working on April 30. We have no plans to continue support.
Looks like the era of interoperable messaging services is over...