Your question seems to be somewhat confusd in a number of ways. Firstly, although we hear about Joel's capture in Chapter Eighteen, the rescue attempt only occurs in Chapter Nineteen. Secondly, Rosh and Malthace have nothing to do with the rescue attempt, that is carrried out by Daniel and his followers. In fact, it is Rosh's complete indifference to Joel's fate in Chapter Eighteen that acts as the catalyst for Daniel breaking with Rosh and his group of rebels.
Chapter Nineteen therefore details Daniel's rescue attempt and the way that it is only successful because of Samson's sacrifice of his own life for its completion. Note what Joel tells Daniel and the others about Samson's vital role in his release:
It was Samson. I thought at first it was another slide coming down, and then he was there. He threw you onto the rock. Right over his head. Then he got hold of my chain and twisted it open with his bare hands, and he pulled me free and threw me up on top of you.
Thus we can see that Joel was successfully rescued from his fate of working as a slave on the Roman galleys, but only at a great cost--the life of Samson.