How long can an elderly person live with Aortic Valve Replacement and a bypass?

Does anyone have a parent with an Aortic Valve Replacement and bypass?
My mother had the open heart surgery three years ago and died recently from heart failure and stage III colon cancer but the doctor said the real cause of her death was her heart. She was 87 years old.
She went through the operation at 84 years old and recovered fairly well the only complication she had post surgery was kidney insufficiency but it resolved.
The quality of life wasn't great medications gave her a lots of side effects and she was always complaining at how unwell she was. Cardiologist didn't take much notice of her when she complained and kept saying that the pain she suffered in the back during activity was arthritis of the spine, to me the way she explained it it sounded more like angina symptoms.
She didn't enjoy food very much and her emotional state was very low.

I would like to hear your experiences with this kind of operation in the elderly.

Thank you.