Do bear in mind that if a member of traincrew is missing, then their train(s) will be cancelled, but everything else will run; there is (presumably) still the option of switching traincrew around at the last minute so that the least important working ends up being the one that is cancelled. If a signalbox is closed because there is no signalman, then the whole service over that line stops.
As a signalman I have gone in when feeling foul and stuck it out. On one occasion I told the management that I would finish the shift but wouldn’t make it the following day; on another I rang in as soon as I booked on and said I wanted relief because of toothache: they found somebody in under two hours (I was off for a week because the dentist messed up). Signalmen know, or used to know, just how vital their presence was to the railway’s operation and wouldn’t miss out willingly. Nor would they dump the signalmen that were waiting to go home in it. One is the way to difficulties with the management, the other leads to unpopularity with your workmates.