I would still make sure they do biopsies. They are simple to do and are the only sure way to know if the cancer is still present. I would also spend some time with them discusing the lymph nodes. Keep in mind that the treatment must kill all the cancer. Not 98% but 100%. Any cancer that remains will grow again and kill him. If the doctors are not sure they have achived 100% eradication of the cancer, your job is to find what you can do to get to that point.