How about a sentient AI whose utility function is orthogonal to yours? You care nothing about anything it cares about and it cares about nothing you care about. Also, would you call such an AI sentient?
You said it was sentient, so of course I would call it sentient. I would either value that future, or disvalue it. I'm not sure to what extent I would be glad some creature was happy, or to what extent I'd be mad at it for killing everyone else, though.
Thought experiment:
Through whatever accident of history underlies these philosophical dilemmas, you are faced with a choice between two, and only two, mutually exclusive options:
* Choose A, and all life and sapience in the solar system (and presumably the universe), save for a sapient paperclipping AI, dies.
* Choose B, and all life and sapience in the solar system, including the paperclipping AI, dies.
Phrased another way: does the existence of any intelligence at all, even a paperclipper, have even the smallest amount of utility above no intelligence at all?
If anyone responds positively, subsequent questions would be which would be preferred, a paperclipper or a single bacteria; a paperclipper or a self-sustaining population of trilobites and their supporting ecology; a paperclipper or a self-sustaining population of australopithecines; and so forth, until the equivalent value is determined.