Grown children often secretly wish for an aged parent to die. And it’s not necessary for the parent to be a witness for the prosecution. It’s a taboo thought, but common. Particularly if the parent has lost all capacity for joy at being alive.
Even the best parents are doing what they think is best for us. At some point, we have to take over for ourselves.
All you can do as a parent is try to pack the days with as much good stuff as possible and hope that it outweighs the bad. You hope that the good stuff sticks.