In New Zealand immunotherapy is not funded by our free medical system but some people pay for it privately. I don't think insurance covers it to any large degree. Form my understanding it is only effective for 20% of head and neck cancer patients but much more effective indeed for people with melanoma and other cancers. Your fiancé seems to have a rarer type of HNC so I shouldn't really make any suggestions. P16 + cancers probably react better to chemoradiation. One such patient in my group has had a good outcome from Keytruda and targeted radiotherapy to the mets in her lungs. These days radiotherapy is more targeted and sophisticated. You could ask more about this. There is also Proton therapy with fewer side effects.