Ivan is confronted with almost unimaginable hardship, and at several points consciously chooses survival over death. For instance, he winds up in prison in the first place because he lies and claims to be a spy for the Germans, when in fact he had simply been captured by them while serving in the Soviet army. Had he claimed to be an escaped prisoner of war, he likely would have been shot. Once in the prison camp, he labors, and survives, under conditions that kill many of his fellow prisoners. He manages to survive by just doing enough work to avoid the ire of camp guards, doing additional work to get food at the end of the day, stashing away bread inside his mattress where it will not be detected, and currying favor with the gang boss. Above all, he maintains his dignity and his mental health, both of which, we learn early in the book, are essential to survival in these unspeakably harsh surroundings:
If you’re working for human beings, then do a real job of it, but if you work for dopes, then you just go through the motions. Otherwise they’d all have kicked the bucket long ago. That was for sure.
Solzhenitsyn thus explicitly links survival to maintaining one's humanity. This is the overriding theme of the story, that even in a system designed to destroy it, man can maintain his dignity, which is in fact a precondition for human survival.