The answer depends on whether there actually was an error committed by the District Attorney. Was your son actually protected by the restraining order but there was a clerical error? Based on the facts your provided, that is the only seemingly plausible error that might subject you to liability. However, it is not up to your wife whether the DA will reopen the case, it is simply up to the DA. It sounds as if your wife is trying to exert leverage on you that she does not have; however, an attorney would need more facts to say for certain. If your wife does indeed have concrete evidence that the DA made a mistake in dismissing the charges (which does not seem likely), then the DA does have the discretion to reopen the case. Again, an attorney would need to know more concrete facts to give you an accurate assessment.