In Chapter 18 of The Bronze Bow, do Malthace and Rosh manage to get Joel out from the galleys?

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:

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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.