Early in Staubach's career, Tom Landry would go back & forth between Staubach & Craig Morton. He did it routinely in 1971 & the Cowboys made it all the way to the Super Bowl, but lost to the Colts. They eventually traded Morton to the Broncos & Morton took the Broncos to the Super Bowl (But they lost to Staubach & the Cowboys).
Let me nitpick about your memory there. Staubach was not inserted into the offense until 1971 when Landry went to the rotating method for the first seven games of that year. For those seven games, the Cowboys went 4-3. Landry then realized the alternating quarterback system was not working and switched to Staubach full time. They won the remaining 10 games (including the Super Bowl).
Nitpicking again: the Cowboys traded Craig Morton to the New York Giants in 1974. I seem to recall that his first game as a Giant was against Dallas. After the '76 season, New York knew they had a winner in Joe Pisarcik and sent Morton packing to Denver where he led the Broncos to a Super Bowl (anyone know whatever happened to Joe Pisarcik?
).
This, of course, has no impact on the 2007 Arizona Cardinals. I like this environment for Warner and Leinart, and I see good things ahead, but then, I'm predicting a 16-0, I mean a 15-1, no I mean a 14-2 season!