Jill,
I have to ask are you more scared for you or for him? It sounds to me like they are pulling out the stops to treat the disease - very agressive treatment and by no means palliative. Yes his life will be different, almost all of out lives are different after this - even those who got away fairly unscathed.

This is a gift for you to give back to your parents who gave so freely to you. That doesn't necessarily mean that you personally have to be the primary caregiver but you must certainly make sure that he has a good one. I am sure that he would rather be in his own environment rather than burdening you.

I had to manage my fathers meds and it was so confusing I put together a schedule in .xls (Excel) database to keep track of it all.

Treatment is very tough at any age and he will need a lot of time resting while going through an extensive healing process. We patients almost always all suffer depression - there's meds for that.

Like Marica said, take a deep breath. There's anti-anxiety meds for too if you need them.