Now that you know the deck should have been permitted and inspected, you will have to disclose this fact to any future buyer. If you do not do so, and somehow sell the house to someone who does not have an inspection, and there was an accident, possibly a serious accident, you could be held liable not only for the accident but face additional penalties because you were aware of the defects and did nothing to correct them. Take your medicine now -- much cheaper and less risky in the long run. Be aware in the future that you should always call the building department to determine whether or not any repair or improvement to your property requires a permit.
It is not a question of fines. it is a matter of safety. And Liability. If anyone was hurt by a deck built without permits, your insurance company would not cover it because they do not have any legal notice (building permit)
My guess is that you will need to bring the deck to code. Most transactions require that any work done during escrow be completed by professionals. My guess is that you do not qualify, so the inspector may require further re-work until it can be approved by the building inspector.