My uncle had NETs in his pancreas, so the issue was in a slightly different location. Bile duct surgery is a massive operation. It's one of the biggies as far as ops go. It usually (maybe always, but not 100% on that one) involves the removal of some of the liver, and damage to other organs is also a large risk. My uncle was fit, but he was still deemed very high risk for a Whipple procedure (the removal of some or all of the pancreas). There are also a lot of major blood vessels in that area. It's usually one of the main reasons why cancers like your father's and pancratic cancers tend to be deemed inoperable because the tumour is in very close proximity to major blood vessels

As far as the chemo goes, i have no idea about that at all. It's maybe a question you can ask the treating doctors. You, or more to the point, your dad, is entitled to a second opinion. Always seek a second opinion if you have doubts. Not saying it will change anything, but it removes a lot of the uncertainty so you won't be beating yourself up for the rest of your life over the should'ves, could'ves and ifs.