Dear George,
if the Priss-Goedel-Priss theorem is right, then the mathematical structure that corresponds to the physical universe is made up of sets and functions (as in Tegmark's MUH), and the latter are total and computable, hence they can be implemented by Turing machines (conputable) that are guaranteed to terminate on each output (total). Now, I am not completely sure about what you mean when you write "do you worry about the halting problem?". I see two possible interpretations of your words.
1. You allude, perhaps humorously, to our own existence, or life span, which, according to this view, should also terminate, without hope for some eternal existence. If this is what you intended, I just observe that there is of course no direct connection between the guaranteed termination of the computations of those defining functions and the presumed termination of our lives. The implied gap is indeed as large and obscure as the gap that separates the static universal mathematical structure envisaged by the MUH and the accidents of the history of the universe that have led to, say, the evolutionary biosphere. This is, in my opinion, one of the weak points of the MUH.
2. Alternatively, you might have intended that the 'existence' of undecidable problems/functions is undeniable (e.g. the halting problem), and it would be unwise to 'rule out' them from our 'real' universe. Well, Priss would question the above terms 'existence' and 'real': he thinks that these functions do not 'exist' in the 'real' universe - the one where SAS arise - and do not contribute to its definition.
In any case, the boss of the agency clarifies, later in the story, that a model of computation that is Turing-universal must include partial computable functions, that are undefined/divergent for some input. Priss's universe, then, would not be based on Turing-universality, which is probably one of the reasons why the agency boss disagrees with him...
Thanks for your comments. Ciao!
Tommaso
PS
I'll read your essay a second time before commenting.