I get that a gorilla is more likely to stand his ground, especially if it’s a silverback and he sees the bear as a threat to his pack. But I see the scenario where the bears deems it not worth it and leaves more as a “fight not happening” rather than “gorilla wins the fight”. Since the question implies a fight is taking place, I’d exclude this scenario and assume they must fight tooth and nail. And if that happens, I bet on the bear.