The route your ENT is taking seems appropriate. Management of a clinical unresponsive or reminiscence HPV nodal disease may be controversial as to who may benefit, as most HPV lymph tumors after curative chemoradiation treatment may be negative upon dissection, which otherwise is thought to be positive, to my understanding. That's why in recent years there are not as many "planned" neck dissections after treatment for HPV oropharyngeal cancer, which would otherwise be automatic, and may not consist of the type of management and consideration as yours is being based on testing, biopsy, palpable exam, nodal level and other considerations. Even the post treatment testing the wait period is usually more like 12 weeks or 3 months due to the inflammatory responses, and have waited 5 months once myself due to an enlarged node, but I can understand your ENT not wanting to wait for a potential tumor attaching to a structure. They also like to keep the whole treatment plan to 100 days for better responses.

HPV nodes contains more cyst fluid to my understanding, can increase in size during treatment, so just the lymph size may be difficult to determine residual tumor. Even the pathology post treatment is more difficult. I've had positive nodes by US FNAB, containing mixed and cancerous cells, that were found to be negative after a dissection, but cancer was found in my case in an unexpected area, neck muscle, from the pathology from the radical neck dissection. The reason for a radical neck dissection was during my surgery, everything was all twisted together from prior radiation, so that may be why your ENT said surgery can be 3 hours if uncomplicated, more if it's more extensive like if a flap is needed, carotid involvement, etc. A RND, which takes more surgical time, usually has more morbidity than that a modified radical neck dissection, due to the neck muscle removed, so a modified radical or Selective neck dissections are more common these days, and preserves one or more structures such as the neck muscle, nerve and vein. I was always happy after my surgeries to get a tumor or anything even suspected to be removed, as I once heard, the key to survival is controlling the nodes, and I keep that in mind.

Even after 5 neck dissections, and 4 radiation treatments my arm movement was still preserved, but there is a need for lifetime stretching, exercise, and have been through PT several times. It wasn't until my 5th radiation, and to level V lymph nodes, brachial plexus, that effected my arm movement, but everyone is different, as areas involved, and so are the surgeons experience.

Good luck with everything.