The rules & terms have been rewritten for the merger. If you log on to your WorldPerks account and go to your E-Certs - click on the SWU certificate to read the rules & regulations. They've changed. I believe you are now able to book them on DL operated flights.
As for honoring them...I have full expectation that DL will honor these through the expiration date. And from what I'm hearing it won't be until March 2010, at the earliest, that the inventory systems are completely combined and still nwa.com may remain operational for a short time thereafter.