I'm not qualified to answer this very serious question. You may want to read these two posts by Chrisb1 regarding fasting and surgery.
Here is a quote from this one: "there is no doubt that fasting after surgery will greatly accelerate the healing process, and especially to the wound where the incision has taken place" //www.curezone.org/forums/fm.asp?i=1538892#i
My feeling is that a very long fast before the surgery may not be wise since you will not be fasting to heal your body in order to avoid surgery. The long fast will leave you with toxins in your blood stream during surgery. This would not be good. You may also be in the middle of a major healing crisis when it comes time for the surgery which would be too hard for your body to handle during the surgery. As I said I am not qualified to give a professional answer. I am just giving you my feelings and opinion. If it were me, I would try to eat very healthy before the surgery and fast after the surgery to accelerate the healing process. I wish you the best during this difficult time.