I realise the situation around rescuing with blocked up trains, more so now you mentioned it. It was very much a speculative thing. I suppose we can blame the people many many many years ago for giving us top contact third rail before any other option came around.I suppose more mpvs could make a difference but then you need the drivers to operate them of youre doing more trips.
The general rule for most tocs where a failure occurs is for the train behind to assist. You could in theory have a rescue locomotive instead but if a train is failed and blocked in by others as generally happens getting any locomotive to site isn't easy.
The only real way to avoid ice problems with third rail is to box it in or make it side contact, the costs would be very very high to achieve that.
I thought about having stronger batteries on existing units than just the shunt ones, but then it comes into the high cost of those batteries and maintenance and replacement so that is not viable either.