They are making decisions in the presence of the knowledge that essentially identical "god" agents will be making decisions based on the same information and th

They are making decisions in the presence of the knowledge that essentially identical "god" agents will be making decisions based on the same information and the same mental states, and that the "god" agents' decisions will impact their own existence. If at any time they were to "choose" to shut down the simulation, it can only be because the total state of the world, including their sense-data and internal mental states, cause them to do so. If that's true for them at time T, then by hypothesis it's true for the "god" agents as well. It may be that, in the sense you have in mind, the protagonists simply do not have choice.