Most prototypes were crushed / dismantled. There appears to be only 3 left. This is 1 of the 3.
A mule is a car that has the drivetrain (electric motors, inverters, various control units, battery pack, etc.) from the Fisker, without having the Fisker body on it (for longer established carmakers, they typically use older car models from the same line). Usually these are grafted onto an existing platform like the Chevy truck in this case. A good example of this, is the upcoming mid-engine Chevrolet Corvette. The mule for that car was a 2014 Holden Ute with the running components arranged in the bed of the vehicle. (Here's what that looked like.
For Fisker, there were other mules / test cars, but a large majority of them were either scrapped, crushed, or sold to private collectors.
Cars a typically crushed by manufacturers for a variety of reasons.
1. They don't meet US regulatory standards, so they cannot be sold like a regular car.
2. They need the space, and cannot store the vehicle.
3. The vehicle has served its purpose and is being eliminated.
Typically, unless the drivetrain/technology features critical IP, most auto manufacturers will sell to a select group of private buyers. These guys and gals typically purchase prototype cars that were made specifically for major car shows, however they will purchase a mule or test vehicle if the right opportunity presented itself.
If there is critical IP on the vehicle, the vehicle usually has its critical components removed for further evaluation, and the rest of the car is either scrapped or crushed.