In re-reading the press release, United promises nothing more than this:
United has reserved a percentage of Saver Award seats on every flight to every international and domestic United destination through March 15, 2007, the end of United's current ticket booking window.
http://www.united.com/press/detail/0,6862,53864,00.html
While it would be easy to infer that United would continue to make seats available beyond March 15, 2007, it's not spelled out anywhere that I saw.