Except as provided in Rule 121, an action shall not be dismissed at the petitioner’s instance save upon order of the court and upon such terms and conditions as the court deems proper. If a counterclaim has been pleaded by a respondent prior to the service upon the respondent of the petitioner’s motion to dismiss, the action shall not be dismissed against the respondent’s objection unless the counterclaim can remain pending for dependent adjudication by the court. Unless otherwise specified in the order, a dismissal under this rule is without prejudice.