I suppose “Gorn just die very quickly in the cold” is the simplest explanation, but still leaves a lot open.
I’d love for Hemmer to return, but feel like the sheer height of the fall makes it quite conclusive that he’d die. Maybe I’ll “warm” to the idea (see what I did there?) if the writers can make it work reasonably. It would be particularly fitting if Hemmer’s unique physiology was the thing that means he can survive, as his preference for the cold is the opposite of the Gorn, and he even says “Just like Andoria!” before he jumps jumps off. Maybe if Batel is able to be saved from her Gorn infection, the new medical knowledge could be used to save Hemmer if he is indeed semi-frozen/hibernating or something. It could make for some interesting further development of the Aenar race also.
The possibility of revisiting the specifics of this episode could be why they’ve left these loose ends that I’m questioning in the OP.