Do we get cash or goods if we save citizens?
Every citizen you save drops an amount of gold equivalent to what a white mob in the current act/area/difficulty would drop, complete with the randomness that entails. Sometimes you can get thousands of gold for saving just a few citizens.
You also get a small exp bonus at the end of the quest depending on how many you saved.
I noticed also; that completing this event on A2 Inferno anyway, that there's a chest if you follow the civilians into the sewer after the event is over. I'm unsure if the chest is random, or if the # of people saved determines the quality (I definitely didn't save them all), but I honestly haven't even checked up until this last playthrough.