I understand that science exists to make predictions, and that "unitarity" (the 100% total of the probabilities of all possible outcomes) is a major factor in the morale of scientists.
However, in a "temporal multiverse" comprised of local universes that are no longer in causal contact with each other, I'm not sure that Hawking radiation would be essential in maintaining unitarity, since the heat necessarily radiated could be radiated into incipient "local universes" being formed within regions (black holes) that had accumulated radiation and matter prior to the disconnection of the causality within them from our side of the apparent horizon that would form when the escape velocity from them would've reached our speed of light in vacuum (which, given the fact that any BH comprising one of the aforementioned regions would have relatively dense contents, would be much higher than theirs would subsequently appear to be).
In an environment at least marginally eternal to the past, such as Nikodem Poplawski's "Cosmology with torsion" or Aguirre and Gratton's "Steady state eternal inflation" (vetted by Vilenkin in "Arrows of time and the beginning of the universe"), it appears to me that any outgoing radiation might be balanced by radiation absorbed from its surroundings, so that the evaporation of BHs might have little effect on the computation of probabilities, even in civilizations adept at collecting and analyzing stray radiation from intergalactic voids.
I haven't been able to find a motivation for the postulation of Hawking radiation except as a hypothesis which appears to sustain the consistency of quantum mechanics. I might be making a number of wrong assumptions here, so I would appreciate it if the readers could help me by pointing them out.