It seems to me like the OP states, that there does just to seem to be
any contingency plan for what is, unfortunatly, a regular event.

When I was an old fashioned guard at Manchester Piccadilly in the
early 80's the contingency manual for a blockage of all four lines
south of Rugby was like the Encyclopedia Brittanica and everybody new
what to do when depending on exact circumstances.

Also if all the managers and high grade supervisors had gone home then
a van was sent round to bring them all back again.

But then of course, those were the days when, if such an occurance
happened Piccadilly - Euston trains simply had a diesel hung on the
front and off they went vis the Dore curve and Derby to St Pancras.

Plus ca change (sorry I don't know how to do accents)