We have to accept that Gorn biology has no tolerance at all for subfreezing temperatures. The Gorn young are functioning at an instinctual level, they would learn by lethal experience. Unlike the adult Gorn in 2 x 10, they would not have the protection of environmental suits.
As I would very much love for Hemmer to be somehow still alive, having survived the fall and a period of low temperature semi-hibernation, anything that brings Starfleet back for follow up would be welcome.
I’m going with assumption that the plan to lure the more developed Gorn outside was successful, but could not address any new ‘infections’ in survivors. Hemmer repeated the plan, but as an Aenar, evolved for extreme subzero temperatures, and more physically robust than a human, there’s no reason to believe he died, no matter that he was willing to sacrifice himself for his shipmates. (I’m willing to go with his using his abilities and some kind of sharp tool to stop his fall and find a crevice to hibernate in.)