It’s a very difficult decision, to have major surgery in your 80’s. I would consider his mobility, unfortunately a lot of elderly patients mobility really suffers after a spell in hospital, also risk of delirium which is very distressing to witness.
i can only speak from experience, my late MIL, 86, had breast cancer, SIL did not want her to have surgery, as she was concerned the cancer would spread, she worked in a clinical profession.
MIL decided to have the surgery, very sadly after the op the cancer spread very quickly, she was a very fit lady before, she became depressed after the op, recovery was slow, had radiotherapy but sadly didn’t help. I miss her every day, we were very close.
i am so sorry for what you and your dad are going through, I do hope he has a better outcome. Wishing you all the very best.