One of the things I have learned about cc, is that everyone is in the dark. There seems to be an agreement that if the tumour is only in the bile duct then a resection is the best option. Otherwise we are all guessing.
CC is a rare disease and there is little incentive for the pharmaceutical companies to invest in drugs that are specifically for cc. Most of the drugs used for cc are primarily used with other cancers and there is little evidence about their effficacy for cc.
The standard seems to be gemcitabane but if you read the different regimes that people are on, you will see that many other drugs are used, either singly or in combination. Even so the difference that chemo makes is limited and my husband and I ask ourselves if the side effects are worth the gain. ( a couple of months??) Gemcitane is apparently 'well tolerated' and has few side effects but other drugs oxaliplatin Cisplatin apparently have quite severe side effects.
My oncologist said that cisplatin was well tolerated but the nurse on the trial told us to avoid it if possible. Having said that it may work for your father, since all of these drugs have different effects on different people.
Speaking personally and I hope I am not speaking out of turn, I would question whether or not chemo with the side effects they may have, plus regular hospital visits with all the stress that means, is the right route for a 79 year old man.
I hope you find the solution you are looking for and I wish you and your father all the best.