Most of the criminals and predators will stay behind. You can't get on a bus with guns and loot. I would like to add that these predators PLANNED to stay in the CITY and LOOT IT THE ENTIRE TIME. This isn't SPONTANEOUS looting. They should be shot on sight.
I have noticed that we haven't heard much about banks being looted. I don't know anything about safecracking other than what I see in the movies. I suppose the thugs might need some electricity for tools to drill into it or something.
I've been thinking for a while that the gangs started planning this before the call for evacuations even went out. They were better prepared than the governor.