Define 'a good chance'. 15 year old school kid, not doing anything illegal at the time that we know of. A melee breaks out for whatever reason. Those things end in death a lot less often than than gunshots. We have Zimmerman's word that he was about to get beaten to death. Rather convenient.
This was not a home invasion. What likely happened was that he lost his cool and it ended with a killing because he had a weapon he had to use for fear that it would be wrestled from him. Again, no evidence that Zimmerman was even in the right or who started it.