Fna of enlarged cervical node showed atypical cells. Dr. Wants excisional biopsy. What are the chances that this is cancer?

Good chance. Fine needle aspiration (fna) shows atypical cells, means, there is a good chance it could malignant, only way to prove or disprove is by removing the entire node for biopsy for the final diagnosis.
Possible. There are many things that can give you enlargement of the lymph nodes- eg- lymphoma, infection, metastatic cancer to lymph glands from head&neck area etc. Fna has high false negativity, so when fna was done and showed an atypical cells-an excisional biopsy needs to be done to establish diagnosis.Adequate tissue-if possible the whole lymph node- will be needed to make a correct diagnosis.
It depends. Usually, head and neck cancer presents by age 50. This is a rare finding and the node is rock-hard and painless. It would probably be unable to yield anything on fna. But the node could be from cancer metastasis. It could also be infection since many things beside cancer can cause atypical cells. Other tests would be needed, like tumor markers, and more history. It can be anything.