Battle of Alesia question?

I am doing a report on the Battle of Alesia and have a question regarding whether the movie Julius Caesar is accurate about the fall of Vercingetorix. Did he actually ask Caesar to kill him? The movie part doesn't make sense because his reasoning for being killed did not make very much sense. He said something about wanting his gods to live on with him people, but why would he have to be killed? Would he fight back if they kept him alive? Did Caesar keep him alive like in the movie? Help please! None of the research sites say anything about it.