If a premenopausal woman underwent a hysterectomy with unilateral SO with final pathology demonstrating an intact mucinous borderline tumor with negative washings, would you take her back for surgical staging?

No, I would not take her back. NCCN guidelines affirm that a patient with incompletely staged, or incompletely resected borderline tumor may be observed if CT chest, abdomen, and pelvis reveals no residual tumor. Surveillance should be sufficient.