A 38-year-old man is undergoing left total thyroidectomy for multinodular goiter. After careful dissection and identification of the left recurrent laryngeal nerve, the surgeon ligates the superior pole vessels. Immediately after ligation, intraoperative neuromonitoring (IONM) shows loss of signal on the left side (no electromyographic response to stimulation). The right side signal remains intact. The nerve appears visually intact with no visible transection or crushing. What is the most appropriate next step?