SLF, my experience was tongue cancer, spread to several lymph nodes. You didn't mention where the primary was but from your post I'm assuming it was tongue.

Getting follow up radiation will probably increase the probablility of long term survival by a large percentage. Side efffects can be reduced by the type of rad done, XRT where there is a wide beam approach vs IMRT where the beam is aimed specifically at the tumors and manipulated to miss such things as salivary glands etc. Chemo, mainly Cisplatin is used as an addition to help the radiaton do it's job.

I had a recurrance about 6 months after finishing treatment for the first surgery, the cancer had spread to the opposide side and gotten into 2 lymph nodes. Surgery again followed by IMRT and Cisplatin, recommended by the doc to stop the spread hopefully once and for all. I'm a year plus post that treatment and last scan was a-ok.

Unfortunatly, from what I see treatment seems to vary country by country, and at least in US and HK (where I had treatment) surgery is almost always followed by rad+chemo to stop any spread.

I'd advocate to the doc do to the rad+chemo. In this battle you want all the weapons you can get ahold of. Just My Humble Opinion.
Bob