I don't follow how this is an argument against cryonics, unless you're talking to someone who really truly believed that cryonics meant a serious chance of actual literal immortality.

(Also, I have seen it alleged that at least one plausible model of the future of the universe has it dying after finite time, but in such a way that an infinite amount of computation can be done before the end. So it's not even entirely obvious you couldn't be subjectively immortal given sufficiently advanced technology. Though I think there have been cosmological discoveries since this model was alleged to be plausible that may undermine its plausibility.)