Although Lex had expressly hired these workers for the purpose of fighting, and they had a bloodline that was for the express purpose of coming back to life, he did not want to force anyone. Even though he said he wouldn't be giving them another chance later on to quit, if one of them really wanted to, Lex would figure something out.
Besides, he had seen enough of the universe to know that anything was possible. Even if they had a bloodline that could revive them, who was to say there wasn't another bloodline out there that could perfectly counter this ability? Since bloodlines were based on laws, what if they encountered an enemy who had a better mastery of the laws that this particular bloodline was based on? Couldn't they theoretically counter, or even control their bloodline?
Lex didn't have the answer to such questions, but he knew that it was best to give them as much choice in this matter as possible.
