Just saw your post, and wanted you to know you are not alone here-Don·t know what time ite is where you are, but i think it may be a while before there are others on line who have been in the same situation as your Dad, or you as a caregiver. I guess your Dad is very afraid at the moment, and in his own way he is dealing with it by trying to face the worst case scenario, and his main concern is for the welfare of you and your Mom.
A cancer dignosis, never mind the idea of undergoing major surgery, is frightening for anyone, patient or caregiver, but there are many on this site who have been through it, and come through after surgery with a pretty good life. I wish I could answer your question, but I can·t, other than say carry on being positive, and realise that he needs time to deal with what is happening. I am sure others who have been in the same situation will post soon,but in the meantime , stay strong.
Diane