Escaping is one thing (definitely an option, but you're running down a straight aisle that makes you an easy target - Holmes apparently shot numerous runners). Taking the shooter down is another thing entirely.
The cops shot hundreds of rounds at the North Hollywood bank robbers (who were if anything LESS armored-up than James Holmes - they didn't have helmets - much less riot helmets - throat protection or leg armor, as Holmes did), but they kept moving and kept shooting back.
I don't see it as realistic to think that civilians with 6-18 round (usually 10 or fewer) pistols, shooting in the dark, in a closed room full of tear gas, could possibly stop this particular shooter. If they did it would probably be luck (e.g., hitting a tiny gap under the riot helmet's visor) as much as skill/training.