No war 'on terror' can ever be known to be won. In the absense of any terror, one might assume it won, but the very next terror attack will prove him wrong.
Just because such a war cannot be won, however, doesn't mean it shouldn't be fought. Most of us would admit we can never win a war 'against murder' (there will always be killers), but it doesn't mean we stop trying to catch murderers.
Having said that, there are more effective ways of fighting such a war than trying to 'build democracy' (by which they really mean liberal democracy, which in a country of hardnut Muslims is as close to hopeless as you'll get).
Ending immigration and policing more closely our domestic Muslims would be a far more effective way of 'fighting terror'.