Normally, a confidentiality agreement creates a trade secret (and must qualify for trade secret treatment which basically means that measures are in place to keep the secret and that the secret has economic value), and so long as the confidential information described in the agreement remains secret, that can have an indefinite duration, even in the absence of a copyright or trademark.
As a general rule, unless the contract provides otherwise, a confidentiality agreement's protection of certain information does not expire. But, with the passage of time, it may get harder to show the elements of injunctive relief for a disclosure (e.g. "irreparable injury"), and the damages for a breach may become nominal, perhaps even to the point where a liquidated damages clause for a breach of the agreement in that particular way becomes contrary to public policy as a penalty not reasonably calculated to substitute for actual economic harm. Also, the doctrine of laches could conceivably apply to bar a claim under the agreement if the passage of time in enforcement of the agreement renders it unfair, or the doctrine of waiver could apply if other breaches were consistently ignored.
If you disclose the information anyway, and no one sues or brings criminal charges within the statute of limitations for a trade secret violation, then the breach of the agreement with respect to the disclosed information is no longer actionable.
Since many statutes of limitations run from discovery of the breach, and disclosure of confidential information could conceivably trigger a suit against the company for some reason, the economic value of keeping the original secret could continue long after the intrinsic value of the secret has expired.