Just a layman's guess here, but I strongly doubt the bystander effect is strong enough to overcome the chances of a single person helping. Note that for the bystander effect to happen, all the people in the vicinity have to not intervene, while for it to be defeated, it takes a single individual to act.

I doubt that as N increases the "network" effects are strong enough to overcome the chance that someone that will help, regardless of what the effect of "N-1" bystanders is, shows up.