It was discussed in the Naruto anime (episode 66), the jounins stated that Shika had great leadership skills. They commented on how his giving up boosted his leadership skill. They supported this my using the premise "I completed my mission, but lost my whole team in the process." The jounins thought that this would never happen to someone like Shika (i.e. Shika would never allow it). Yet, it is actually happening. Chouji, Neji, and Kiba may be dead. The only ones left are Shika (himself), and Naruto. This contradicts every premise that enabled him to become a chunin.
So I ask you, how did Shika become a chunin? The only answer I could find that would satisfy everything that has happened, is if none of the team members are dead.