Well you lot appear to have all the answers
perhaps you should write to Southern to tell them just how to respond. From experience I can tell you that the first train affected would not necessarily know the shoes were off. Only when a train loses all power will it be known that something major has happened. Then its line blocks, trackside inspections, telling the relevant parties, assessing the scope of the situation, agreeing a decision, getting all the relevant staff of several different organisations together, briefing them, getting them on site, blocking all the lines and turning off the power, then marshalling hundreds of people out of trains without a platform into an environment that is not designed for them without slips or trips, then find space for them all somewhere because no platform or concourse is designed to cope with them all arriving at once like that.