Some background: The show was canceled in May, but a 10-12 minute epilogue was filmed during the making of the season finale just in case NBC should decide to cancel the show. No decision had been made when the finale aired on March 30th, so the epilogue did not air.
The special ending has Meg returning home after a 3 year absence in July of 1969.
Now it looks like it will air sometime this summer.
http://www.tvguide.com/news/insider/NBC All-Star Party
7:57 Scoop! It’s the news American Dreams fans have been dying to hear: The alternate ending series creator Jonathan Prince shot but never aired will finally see the light of day this summer, per NBC chief Jeff Zucker. “Thank you for reminding me about that,” Zucker tells me. “I’m going to make some phone calls about that tomorrow. It’s gonna happen.”