There's a legal mechanism for everything. Just because no one has ever rescinded before doesn't mean they don't have the authority to do so, especially considering the circumstances.

They should get legal statements sent to their legislatures indicating their decision to reverse an action made under duress. Indicate that they are pursuing lawsuits against the instigators of the mob, and insist the legislature not certify any results without their consented signatures.

If that fails to get support, get it to a judge.