You've asked several questions and I'll try to answer them from my point of view. Keep in mind that these are my opinions only. Others may have different opinions which are equally valid.
1. I carry for protection of myself and my family. Once I have them, and myself, in a safe place I am not going BG hunting. My name is not John Rambo.
2. Only, and I stress "only", if I am in a position to to prevent the BG from shooting innocents without actively seeking him out will I act.
3. As soon as the police show up, my weapon is going to be on the ground as far away from me as I can get it and I'm going to be on the ground myself. Reasoning behind this is that any police officer responding to an active shooter call is going to be as nervous as a long-tailed cat in a room full of rocking chairs. I do not want him/her to be nervous about me.
4. On the Aurora shooting, had someone ignored the signs and carried into the theater, a lot of lives would probably have been saved. From what I have read of the situation and its aftermath, there would have been ample time to disarm after having neutralized the threat and before the police arrived.
I guess the main point is this: If you are forced into action against an active shooter, you want to be darn sure you are not holding your firearm when the police arrive.