Back in the day, I ran a couple of chatbots on Windows Live Messenger (although it was called MSN Messenger then), so I'm reasonably familiar with how the Microsoft Notification Protocol (MSNP) works. We had a Perl module called MSN.pm which works with the MSNP10 version of the protocol, and it probably still works today.
That's right, the Windows Live Messenger protocol is still perfectly alive and well today. A while back, I booted my Windows OS on my PC where I still had Pidgin set up to sign me into MSN, and surprisingly it still worked. One of my Skype contacts sent me a message over Pidgin, and their "MSN e-mail address" had an "@SkypeDomain.fakedomain" domain part. It seems that now, though, while the MSN servers are still up, they at least block non-Chinese users from authenticating (Pidgin says "invalid response from server").
The Skype/MSN merger was done in a pretty half-assed way by Microsoft:
I don't get why Microsoft doesn't just pull the plug on MSNP completely, and force everyone to get a Skype name if they don't already have one linked with their MSN accounts.