Hi Susan,
Your profile says your cancer was nasopharynx. If that is true, how can it be an unknown primary?
I was diagnosed in 1997 with SCC, unknown primary, with metatsis to one lymph node in my neck. I had a right neck disection, all 16 of my rear teeth removed prior to radiation(dumbest thing I let them do), followed by 36 radiation treamtents, but no chemo. I was a smoker/drinker running scared because I had a very dead friend who had found a swollen lymph node in her neck and was dead 9 months later(hers was a metastasis from breast cancer, but I didn't know that at the time). All I wanted was the thing out and I'd ask questions later.
One of the bad things about an unknown primary is that they have nothing to aim at, so they wind up aiming the radiation at everything from the tops of yours ears to the tops of your boobs, killing all your saliva glands in the process, although I still do have some saliva. Sometimes during radiation, the primary does turn up. Mine didn't. One thing you might consider if the metastasis was definitely to one side, is to have the radiation only to that side. They don't recommend this and it is difficult to do, but I wish I had done it. I do know someone who did this, and he is quite alive and celebrating his 5 year anniversaary.
You also only get to have radiation to an area once as I was loathe to find out when I developed a tiny tumor on my larnyx 4 years later. Since I had already had radiation to that area, I had to have a total laryngectomy.
I am not recommending that you not have the radiation and if it is really nasopharynx, it doesn't sound like an unknown primary. However, if it really is an unknown primary and your willing to play Russian roulette, I'd get a second opinion and also see if they can limit the scope somewhat and protect your saliva glands. Also watch out for those dentists that decide they want pull any tooth that is in the path of the radiation field.
If I had this to do over again, I would have only had the radiation to one side and kept my teeth(I have a second and third opinion from a dentist and periodontis that specialize in cancer patients that say they should never have been pulled). Too bad I didn't get before I let them pull my teeth.
Good luck with whatever you decide.