All the points raised by
@Tom B @Banham7 and
@Magdalia all really come back to the same thing, lack of contingency planning.
Set up a way to allow the train manager to open individual doors irrespective of location. No software interlocks, as systems can and do fail, maybe just a key release behind a keycoded key safe, which can be quickly restored once the incident is over. Deals with short platform issue and overcrowding, somewhere like Finsbury Park opening just two doors would limit the flow of passengers. If the passengers see that something is being done they will be less likely to take matters into their own hands and use the emergency exit handles. If you are worried about the train manager 'getting it wrong' set it up so that the procedure for any out of the ordinary opening has to be confirmed by the driver.
At somewhere as congested as Kings Cross having some sort of 'thunderbird' capability would seem to make sense, either to deal with a failed train or to assist with recovery in the event of disruption, but the bean counters dont like it, and in the current 'race to bottom' railway it doesn't happen.
The 'Balkanisation' of the railways hasn't helped. In the event of disruption 'ToC' should be binned, if the bean counters want to play monopoly behind the scenes afterwards let them, but things like ticket acceptance needs to be the default, not something that has to be confirmed.
There is a lot that could be done fairly simply, but the current structure and higher management (i.e. DfT micromanagement) means it doesn't happen. Incidents will happen, things will go wrong, having a robust plan B in place to cover likely forseeable impacts e.g. Kings Cross platforms blocked by empty trains, which is a likely outcome to a lot of initially dis-similar incidents would make sense.