Is it sometimes normal for an old pet to go away to die?

The other day I met a neighbor who was posting a flyer on the light post near my sidewalk. Her cat of 19 years, poor eyesight and hearing, had wandered off and not come home for several days. The cat had wandered off several times over the years, but had returned within a day or so. The neighbor feared that the cat’s advanced age would negatively affect her ability to find her way home. I think the poor animal wandered off to die. I did not share my feelings with the woman, only assured her that if I saw the cat I would call her.