Note that evolution isn't about individuals, it's about genes (which we should further note is more than just DNA, but that's a different discussion). If it weren't valuable for humans to live at all without being fertile, then the average age of menopause and the average age of death would likely be much closer together. As it turns out, the human genes that were best able to pass themselves along were those that kept old people around despite being infertile, presumably to the benefit of helping to raise grandchildren, among other things.