It got me thinking too, would smaller overlapping ROCs be the solution with one able to cover for another? Would that work and if so how?
You could take it further, and have much smaller signalling centres, let's call them "boxes", each of which has responsibility for a relatively small geographic area, and, to be independent of the need for mains power supplies, could have a revolutionary type of signal which has a moving arm, let's call them "semaphores", connected to each box by metal cables, with points connected by metal rods.
In addition, the block system, rather than rely on computers, could use a low voltage (and runs for ages on battery backup) sort of audible transmitter between boxes, let's call it a "block instrument".
And finally, to really be "off the grid", the signals could, at night, have some kind of burning device to provide a light, let's call it, a "paraffin lamp".
I jest, of course, but just occasionally one does wonder about whether "progress" really is that or not. Have to say though, those paraffin lamp-lit signals were pretty horrendous to see at night.