A 14-year-old boy with known nasopharyngeal angiofibroma is scheduled for surgical resection. Preoperative angiography shows a large tumor fed by the maxillary artery and ascending pharyngeal artery. The interventional radiologist has successfully embolized both feeding vessels 36 hours before planned surgery. Intraoperatively, the surgeon encounters significant bleeding from the tumor bed despite embolization. What is the most appropriate immediate management?