It's completely normal for him to get a bit down. This is very life changing. I'm sure Kris would have had difficulties if we, his family , hadn't been so positive and supportive. There is also the option to start antidepressants . Kris started these in the 2 week post op. they take 3 weeks to kick in, so start now. Kris was only on this medication for 3 months and has never looked back. He leads a full life and I'm sure your Dad will too with all your support and encouragement.
I will say though, , that recovery takes a while. Don't expect him to be back to himself for some months. It took Kris a good 7 months. However I was able to relate him safely home by himself at around the 8 week mark. He could do all things independently by then.
Thinking of you,
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!