My sister-in-law recently had a benign tumour (called a Schwannoma) removed from her lower back, in a complex operation carried ouy by neurosurgeons. The operation is delicate because of the number of nerves that are routed through the spinal column, but rest assured it is only carried out by specialists. Of course, the doctors have got to warn you of the potential downside, but they said that to my sister-in-law as well. She recovered from the op and is now as fit as she was beforehand.
These tumours, whilst benign, can grow to the point where they put pressure on nerves that affect movement, or they can get too big to be safely removed, so it is best to have them removed early to avoid problems later. There are downside risks to any operation, but try to see this as an opportunity for treatment that will remove future risk.
I really wish you and your Dad well.