auto accident in a rental car, declined additional insurance will credit card company or private insurance cover damages

It looks like you have two issues here. The first is, how will you be insured against any action for negligence and the second is, how should you proceed with the possibility that your license will be suspended.
You should take a look at the language of the policies (under liability coverage) of each insurer. If you have a private insurance policy for a car you own, it may cover you for liability while operating a rental vehicle. If you are served with a lawsuit, the best idea would be to send copies to your private insurer and the credit card company insurance carrier.

As far as your license is concerned, I would recommend that you contact an attorney who handles these issues in your area. If you are having trouble finding someone, your local Bar Association should be able to assist you.

As an aside, if you have sustained injuries in the accident, I would not hesitate to inform the credit card carrier and your personal insurance company know so that they can send you any required paperwork for you to fill out. There may be time limitations and you do not want to waive any rights you may have to benefits.

Best of Luck