Josee, glad that you have got his pain under control as that is very important. There is no need for anyone to be in pain.
As for the radical neck dissection, I agree with Paul. Recovery from the surgery is very quick and is usually pretty pain free due to nerves being cut. Discharge is usually the following day.
However the side effects take quite some time. He will need lots of physiotherapy to help with shoulder and neck movement which are the main areas of concern. Please don't delay on this. It is crucial for recovery.
Tammy

Caregiver/advocate to Husband Kris age 59@ diagnosis
DX Dec '10 SCC BOT T4aN2bM0 HPV+ve.Cisplatin x3 35 IMRT.
PET 6/11 clear.
R) level 2-4 neck dissection 8/1/11 to remove residual node - necrotic with NED
Feb '12 Ca back.. 3/8/12 total glossectomy/laryngectomy/bilat neck dissection/partial pharyngectomy etc. clear margins. All nodes negative for disease. PEG in.
March 2017 - 5 years disease free. Woohoo!