According to Delta's new policy, any partner activity, not just a flight, should extend the expiration date. The online date is not always accurate. My suggestion is to email them, this way you have their response in writing. A call will do also. This should confirm that any partner activity will extend the expiration date.
------------------
Earn money back for shopping online --
http://www.ebates.com/index.jhtml?referrer=keithnj973