I did see a very good under-lying theme in the story. There may have been more, but the main one that I got was: Despite our differences, working together/having unity and teamwork is better than fighting each other and separating. Not only in survival situations, but also best for the growth and advancement of a entire world or civilization. Where would we be if the entire world was at peace from the start?
Another good theme was: Even in a team, someone needs to be the leader and make the final call that's best for the group. Others need to follow. Not everyone can be leader, but everyone in the group is important and has something to contribute, if they are Willing.
The SAD truth for both of these good things are that people are selfish sometimes and motivated by different things that are not always good for others, causing conflict and division. These conflicts and issues begin to arise amongst the group of survivors, all-the-while mirroring the entire fate and history of the SANDWORLD.