Megan wanted to fight. She was hoping Martianmanhunter would kill her. She felt guilty for the time she worked for the White Martians and for the Martians she killed. So she wanted to die. MMH on the other hand wanted to save her and he put his faith on her. Thats why he didnt escape even though he could. I agree that there should have been some circumstances that forced the participants to fight but as we saw Roulette had backup plans.