Modified Radical Neck Dissection, MRND, which is the preservation of one or more structures like the vein, nerve and neck muscle, and takes out the chain of lymph nodes in level II-IV, sometimes V.

I always feared surgery, but it was the easiest part of my treatment. I liked it so much I had three neck dissections, two that were radical lol. Sounds like you had Chemoradiation, with surgery as a last resort. It's common that surgery will be needed afterwards, forget percentages, guesstimating 30% range sounding familiar. That's what I had, surgery as a last resort, which sounds bad, but it's not always the case, and mine wasn't. Some have a planned neck dissection after Chemoradiation, which has better outcome in some studies than one that is unplanned. After surgery many go on with no more recurrences, and live normal lives, for us that we call our new normal. All surgeries have certain risks, and so do neck dissections, but some side effects are common, that are doable, and others that are more uncommon. If the doctor didn't think it would be successful, it wouldn't be offered. I went in for a MRND, and wound up having a radical neck dissection, RND, because during surgery my ENT found all my neck muscle, nerve, vein twisted around the tumor from radiation, and had to remove them, along with the lymph nodes in levels II-V. Luckily he did, and not knowing, cancer was found in my neck muscle on further biopsy. That's why your doctor may have said guarded being a neck dissection is more difficult in a radiated neck, and to what extent is only known during surgery. After all my neck dissections, I ate a BigMac meal either that day or the next

Good luck, and best wishes.