This is a difficult situation. I would say something like this can destroy a company completely. So, the first step is to define the scope of damage. If the company determines that the damage is their fault, they may have to close up shop. However, this is not the end of the company. They an buy another company, a smaller one and take their name for themselves and sell their products under a new company (assuming that they corrected the problems). In this way, the company can start fresh without any negative stigma. The PR, then, would have a much easier job. They would advertise a new company without any association of the former company.
In terms of the older company, the PR would only have to apologize and file for bankruptcy.