I think Nebu was making the point that while we normally use utility to talk about a kind of abstract gain, computers can be programmed with an arbitrary utility function. We would generally put certain restraints on it so that the computer/​robot would behave consistently, but those are the only limitation. So even if there does not exist such a thing as infinite utility, a rational agent may still be required to solve for these scenarios.
I think Nebu was making the point that while we normally use utility to talk about a kind of abstract gain, computers can be programmed with an arbitrary utility function. We would generally put certain restraints on it so that the computer/​robot would behave consistently, but those are the only limitation. So even if there does not exist such a thing as infinite utility, a rational agent may still be required to solve for these scenarios.