Your vehicle could still be as safe as it was in its original condition if it has any minor damage such as a baseball sized dent on a rear quarter panel. If the crumple zones are intact, the rails are intact, and the rest of the frame is untouched, then it would be as safe as it was in its original state. The vehicle will not be safe in a collision if it was involved in a heavy collision where the frame is bent, the crumple is crushed in, and all sorts of cutting, welding, and aligning are required.