I can see various possibilities of ways around de Blanc's argument besides bounding utility, but those are whole nother questions.

Can you elaborate on these?

Not with any great weight, it's just a matter of looking at each hypothesis and thinking up a way of making it fail.

Maybe utility isn't bounded below by a computable function (and a fortiori is not itself computable). That might be unfortunate for the would-be utility maximizer, but if that's the way it is, too bad.

Or -- this is a possibility that de Blanc himself mentions in the 2009 version -- maybe the environment should not be allowed to range over all computable functions. That seems quite a strong possibility to me. Known physical bounds on the density of information processing would appear to require it. Of course, those bounds apply equally to the utility function, which might open the way for a complexity-bounded version of the proof of bounded utility.