When Windows Live Messenger is officially retired sometime in 2013, what does that mean ?

Will all versions of the Messenger client...

   ...  not be able to Logon ?

 ... not see their Contacts ?

 ... not be able to send and receive text-based IM messages ?

Or does it mean that the software will not be updated after that, but any Accounts still "living in the old Messenger world" will still be able to talk to each other using IM ?

Thanks

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