In Bread and Circuses Merik states that if the other members from his ship had adapted they are still alive.
"MERIK: And as for my men, those that were able to adapt to this world are still alive. Those who couldn't adapt are dead."
In the end Enterprise leaves the planet. Did they forget to rescue the remaining crew? Maybe they thought it was too much trouble without interfering with the Prime Directive (which I also thought was ridiculous because Merik had told the proconsul everything about Starships, but I guess by the time Kirk knew about this he was already prisoner and didn't get the chance to use any more advanced technology [though it was surprising when he was told to beam down the Enterprise crew he said condition green, I would have thought there would be a "condition red" which meant covertly send help, which would be ok at this point since Merik had already interfered with the Prime Directive]). In the end Enterprise leaves orbit of the planet. I was a bit surprised to see this episode got a high rating on IMDB, I guess there were some good speeches made.