China, not the Fed, has ultimate control over their monetary policy. They can always change their monetary policy and probably will have to. Which is what the discussion is in fact about, if you read the original article.
If the Chinese keep up their peg, holding RMB is equivalent to holding dollars.
If they fail to maintain the peg, the RMB will most likely rise. Most US consumers are already exposed to the downside of this risk - they have expenses which will rise if the RMB goes up (e.g., all the goods they purchase which are made in China).
By maintaining USD peg China has no independent monetary policy - it's monetary policy is directly influenced by Federal Reserve.