And fair comment about track circuits, though I suppose in an absolute block system you could get away without them (notwithstanding that there might be very good reasons why it isn't allowed at some locations).
A very small number of boxes might have no track circuits, but I don't know if there are any left now. As an absolute minimum, you'd normally have a berth track circuit in rear of each home signal, to guard against a train standing there being overlooked. You certainly can't get away without them just because they've failed - they're an integral part of the signalling system and will (rightly) lock other things.
I have, on one occasion, worked a mechanical box (mostly colour-light signals) for the last few hours of a twelve hour failure of the mains power supply. Everything, including the (large) full barrier crossing just outside the box, worked okay on batteries. The first thing to fail was one of the TPWS transmitters, although the barriers were getting a bit slow by then too! AHBs should have batteries that will last a similar period of time, and even if you lose crossing phones, cautioning for every crossing is slow but at least you can still run a service of sorts!
The trouble with lightning strikes is that, rather than just causing the power supply to fail, they have a tendency to fry things and stop them working altogether!