What if the NYFD had helicopters nearby which were capable of putting out the fires in the World Trade Center towers on 9/11? How much of a difference could they have made?
'Capable of putting out the fires'! You might want to have another look at the footage of the buildings on fire and consider just how big those fires were.
Then we get to add a few NYPD helicopters crashing to the destruction caused. Even if you could lift enough water, you couldn't get it to the fire, and the updraughts caused by the fires would make accurate flying almost impossible.
Same issue with taking the people off by helicopter, before that's suggested. Nowhere near enough capacity and you can't get the helicopter in anyway.