When a vehicle is broken, it becomes harder to use. It takes a –2 penalty to its AC, saves, and collision DC, and the DC of all piloting checks related to the vehicle increase by 5. The broken vehicle's Speeds are halved.
A vehicle reduced to 0 HP is destroyed, like any other item. If the vehicle is in water when it's destroyed, it sinks; if it's flying, it falls and everyone aboard takes falling damage.