I am sorry to read this.
I personally would not be happy with the proposed treatment plan. I do urge you to get another opinion , preferably from a Comprehensive Cancer Centre of world renown.
I'm sure someone who lives in the USA will come along soon and point you in the right direction.
Research has proven that these CCC's get better outcomes for their Patients. They deal with these complicated Patients on a daily basis and use a whole team approach with a Tumour Board coming up with the best treatment option.
I wish your Dad the best,
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!