It's all going to depend on how much the contract is worth and the targeting because there are some serious downsides to attacking a contract like that at distance. If it's anything like a regular bounty it'll be nearly impossible to guess that the chopper is the contract. If it's at distance you'll most likely not be getting any money/ammo/loot out of it. Are you going to give away your location and potentially waste rockets or ammo on what's almost certainly going to be a single kill? Are there really that many snipers who can consistently make a shot at that kind of range while you're in constant motion with this game's code?

I rarely get attacked in a chopper at max altitude, and even more rarely get disabled and I think it's for all those reasons. It's just too low reward/high risk.