See this page:
http://www.microsoft.com/learning/en/us/windows-server-certification.aspx
and click on the link "Upgrade paths for Windows Server 2003 certifications". You will see that you can upgrade from your MCSA 2003 into MCSA: 2008 and MCITP: Server Administrator, and from there you can then move to 2012.
I just checked at Prometric, and exam 70-294 still shows in the list of available exams, so I infer that it is not expired.