If the court is unable to make a substituted judgment under § 13-712 of this subtitle, the court may approve a request for the withholding or withdrawal of a life-sustaining procedure from the disabled person if the court determines, on the basis of clear and convincing evidence, that the withholding or withdrawal is in the best interest of the disabled person. The decision of whether life-sustaining procedures should be provided, withheld, or withdrawn shall not be based, in whole or in part, on either a patient’s preexisting, long-term mental or physical disability, or a patient’s economic disadvantage.