Unless they were told they would be release it they stood still, then they are stupid. As it stands they would be trapped forever or at lest until they starved to death. A human in that scenario of being trapped with no hope of escape may chose suicide. It reminds me of sailors back in the day not bothering to learn how to swim as it would only prolong death if they get tossed overboard in a storm.
That's human intuition though. A yukkuri thinks of one thing, taking it easy. When faced with death, it will do all it can to make sure it continues to take it easy, going as far as killing anyone that gets in the way of their goal.
Why do they do that though. Is 'Taking it Easy' so important for them to kill others? That's not easy at all. At least Chen tries to understand things.