If the characters were going to die, it would likely be in this order of likelyhood:
Carmine - kid can't catch a break. Some locust is almost certainly loading the bullet that kills him into a magazine as we speak. If you want to win the war, just draw the Locust into traps by placing Carmine on the field somewhere.
Baird/Cole - equal chance. They have never been playable characters before and generally acted as comic relief. In either case, the death would almost certainly be a "You go, I'll cover you" moment. Baird is the most likely candidate as it would represent the greatest character turn. Alternately, one is killed saving the other in which case Cole would be the most likely candidate.
Dom - the man has nothing to lose. Fighting a war for the species is only personal if you have some sort of connection to the group. Almost all his comrades are dead. His wife is dead. Every patch of ground he ever defended has been lost. If ever there is a suicide mission that has to be done at any cost, Dom is probably your man.
Marcus - the hero of the series. The man may die but he won't do so until moments before the credits roll and even then he will only die if it means saving the species or saving the girl.
Anya - the only girl in the series. She, in a way, represents what the others are fighting to defend. That she is thrust into battle in the darkest time of the most desperate war in human history is little more than a metaphor. The cities have been burned. The soldiers have been exhausted. The conscripts have dwindled. The prisons have been emptied and tossed into the path of the locust. The only thing left to give is the innocent. If anyone is going to survive, it is going to be Anya, because if there is one trope as old as writing it is that women represent hope itself in a narrative.