A 35-year-old male carpenter presents 8 weeks after sustaining a scaphoid fracture of the proximal pole confirmed on CT imaging. He had been immobilized in a thumb spica cast for 6 weeks but defaulted follow-up. He now complains of persistent wrist pain, swelling, and loss of grip strength. Repeat radiographs show no callus formation at the fracture site. What is the most likely complication and the recommended management?