I have no doubt that the Russians, Chinese, Americans, ISIS, etc. all know this: the MoD probably do too. However, this is a political problem: we (not just the UK) are governed by those who put short term financial gain over long-term planning, either by themselves or those in the business world who back them.
More to the point. If I have understood things correctly, there is no facility for one ROC to take over another’s area, even if only sufficiently to keep main routes operating. Nor are there any emergency control panels at major stations or junctions to allow things to be kept moving. If there was a major failure it would be back to talking trains from signal to signal, but if the ROC is out, where are you going to do that from?
I hope I am wrong in my understanding of the current situation, but I fear I am not. If a thing can go wrong, it will.