Hi there... As klo said inoperable isn't a death sentence, and no one can say for certain that he has 1-3 years his cancer may respond well and he may be NED at the end - all they are offering is an educated guess. That said your dad's treatment is standard. It sounds like a lot but most of us who have gone through rads and chemo have 6.5 weeks, to 7 weeks of treatment. I had 32 as opposed to your dad's 35. And anywhere between 3-6 Chemos (same amount just some hospitals break it up over 6 weeks rather than three)

Most of us have had feeling tubes, not all and some keep them longer than others. I was blessed, couldn't use mine so I sucked it up and chugged my nutrition (ensure, boost, whatever you have available there) I finished radiation on may 4 and by the 19th I had had mine removed as I wasn't using it. Everyone has their own experience with rads and chemo, some really suffer, some have an ok time with it, most fall in the middle. Usually things are ok for the first 3-4 weeks, its usually the last two weeks and the two weeks following rads that are the worst. (Radiation is cumulative) To get through it he needs to get high protein, good nutrition, and lots of hydration. He should rinse with flattened club soda (he can swallow it- it helps heal) or a baking soda, water and salt mixture (he can't swallow this) food with taste funky at first then he'll lose his sense of taste, at this point soft bland food are best.
He'll need a hearing test, and a visit with the dental oncologist for flouride trays, assuming they don't pull his teeth.
Chemo for me was nothing, a little nausea that's it, for some there's more nausea. Usually it is the thick mucous at causes problems later In treatment. If he keeps his mouth clean, and does his rinses it will help with the sores.
He needs a good cream for his neck as well.
There will be others along to give you more info. Best of luck our thoughts are with you,