I think they should capture Mary and Lewis and find out Larry was captured too. Then they get together and blow out of there, but aren't very subtle. When they return to base, Sgt. Johnson disgraces them and then the base gets raided and Larry dies, along with some other marines. Then they find out the rebels aren't the only threat, and that there is more to Earth than they had suspected. I'll try to think of more if you don't. Tell if its crap or decent.
This is just a thought.
Whoever said "It doesn't matter if you win or lose" probably lost.