Michele,
While I had a known primary, I had conventional radiation in a field very similar to what Brian described (IMRT wasn't even around then). I also had heard plenty of warnings about quality of life after this kind of treatment, and certainly the months during radiation and well beyond were painful and difficult, with mouth sores, infections, and swallowing problems. However, once my mouth healed, the taste buds returned, and I got quite a bit of salivary function back, the quality of life has been great -- and in some respects it's even better than before cancer.
The key thing for your husband at this point is to have a head and neck cancer team that is experienced and thorough -- this is a disease that you want to hit hard at the first opportunity.
Cathy