As bad as it looks, loosing a spring shackle bolt isn't all that bad as far as creating a dangerous driving situation. It's much like when the spring centre bolt shears and the axle is no longer anchored in one place on the spring, things just feel a bit strange and the back doesn't neatly follow the front, more off to one side a bit, it does make round abouts some what interesting though

Get the mechanic to check the tollerance between the shackle pin and the housing when he comes to replace them, that is the most common cause for the bolt to shear, it gets twisted and high tensile bolts shear rather than bend