Who Will Buy US Treasuries When the Fed Stops Buying?

Bill Gross runs the largest US bond fund and he raises the title question. He believes that the Fed did the right thing when it initiated quantitative easing to replace the funds available for bank lending by the deleveraging that followed the Lehman bust.
The three graphs that he included in this article tells the story. The Fed and other sovereigns have been purchasing the treasuries while private investors have been spectators. In order for the story to have a good ending, private industry must start investing in the economy to produce the economic growth that is needed to keep our debt to GDP ratio in a save zone. Otherwise, the Fed's program of quantitative easing will have been a failure.