My mother died of cancer 11 years ago. There was almost no warning as it was too advanced to treat by the time it was found out.
I took time off work and took care of her at home with the help of Hospice for about two weeks before she died at home. I knew that I had to do that for her, that I would regret it if I didn't do all I could. I bathed and fed her, massaged her with lotion for aches and pains.
When I knew the end was there I told her I loved her and she barely whispered, "I love you." That was the last she said.
When you've done all you can, you let go.