Much of the uncertainty in economics derives from our inability to do laboratory experiments, and that includes uncertainty about which model best describes the macroeconmy.
When the present crisis is finally over, those who advocated fiscal policy, those who advocated monetary policy, and those who advocated no policy at all will all say "I told you so" based upon their reading of the evidence.
Some New Keynesians will cite fiscal policy as the important policy response, and the timing of the policy relative to the recovery will likely support that argument. Other New Keynesians along with Monetarists (e.g. Lucas and others who believe monetary policy can help, but fiscal policy is ineffective) will insist it was monetary policy that saved us. The timing of the monetary policy response will support their position as well.