Whether Rockstar wanted helicopters to not explode after entering "bigbang" or not, this little mod allows you to do so. Any other mod or cheat that blows up all vehicles should also be able to blow up a helicopter, usually a police helicopter.
How to install: Unzip the .asi file into your game folder.
How to use: Try using something that blows up all vehicles, such as the in-game Big Bang cheat, and you will see the A.I. helicopter get blown up.