When individuals have reached a safe spot, law enforcement will likely keep people in that area under the situation is under control. The Department of Emergency Management asks that you do not leave until law enforcement authorities have said its OK to do so. If possible, survivors of active shooter situations should seek out mental healthy professionals for assistance.
What survival in an active shooter situation boils down to is preparedness. Being aware of your environment, gauging the situation, and reacting can play vital roles in your survival and the survival of those around you.