Utility is goodness measured according to some standard of goodness; that standard doesn't have to reference human beings. In my most optimistic visions of a far future, human values outlive the human race.

Are we using the same definition of "human being"? We would not have to be biologically identical to what we are now in order to be people. But human values without humans also sounds meaningless to me. There are no values atoms or goodness atoms sitting around somewhere. To be good or to be valuable something must be good or valuable by the standards of some person. So there would have to be somebody around to do the valuing. But the standards don't have to be explicit or objective.