Your Oncologist will give you all the appropriate answers and I hope I didnt confuse you further. I know that the hardest part of this process is the wait - it can be nerve racking and we are all always waiting for something; for a test result, for a CT scan, to speak to a doctor etc.
Just because he has some potential disease in his lymph nodes (again this is my understanding from your post however please ask your oncologist to confirm) it doesnt mean it has spread anywhere else. Before a Whipples they perform a variety of tests including MRIs etc to check that it there is no visibile spread anywhere else.
It is important during this process that you look at the positive aspects; your father has managed to have surgery that many unfortunately can't and that they only saw one out of nine lymph nodes with what sounds like microscopic disease (however again get the doctors to confirm this point please)
This information is what oncologists use to make a game plan; and I am sure they will for your father.
I hope I haven't created more apprehension and confusion as this is the last thing I wanted to do.
Rest assured that your Oncologist will explain everything in a better manner and importantly will use this information to plan your father's treatment.
I wish all the best for you as I understand how you feel with my father undergoing this process.
All my best