The frog would easily overpower both MC and the gorilla at the beginning of the fight, but I doubt that he would kill them outright. After making sure that their bonds were secure, he would probably proceed to force himself (sexually) on both of them.
After exhausting himself, the frog would surely pass out. At this point, I think it is likely that the chief would be too traumatized to think, let alone try to escape. Gorillas are pretty tough, though, so I think the gorilla in this scenario would probably be able to free itself and kill the frog in its sleep.
Now, having dispatched with the frog, the gorilla could claim victory by taking advantage of the chief in his fragile state, but I think it's more likely that he (the gorilla) would take pity on the chief. The gorilla would then gently untie him and hold him in his strong gorilla arms as the chief weeps silently.
Looking calmly into the chief's visor the gorilla would then whisper "I'll never let anyone rustle your jimmies again."