The FAA can and does assess "civil penalties" (the administrative equivalent of a fine) when suspension or revocation doesn't stop someone from flying. Also, if the person flies in commercial service without a license, they can be charged criminally for violation of US criminal law, and there are major fines and jail time for that, but that doesn't cover noncommercial flying. Finally, the Department of Justice can (at least in theory) bring legal proceedings to jail someone for civil contempt if they continue to defy such orders despite all normal administrative processes, and keep them in jail until the offender convinces a Federal judge s/he won't do it again, although I've never heard of that being done.
