As an aside on Thursday's sketch, let's discuss its safety-features. Rubblepiles seem resilient: where a breach opens up, it should only be localised. A breach in a large solid rock - like Deimos, or Eros or Apophis - might not be.
I don't actually think that the rocks be all that solid, even on Eros. I expect colossal boulders with gravel in-between. The spingrav tubes are each, potentially, subject to blockages. Something might shift or even crack a boulder above or below. In natural milligravity, which at the centre is more like microgravity, a crack should be visible before the rocks lazily intrude upon the passages. Or just an accumulation of regolith and gravel.
Higher-risk would be sabotage, or some asteroid-shaking impact like an experiment or docking-manoeuvre gone wrong elsewhere on the rock. More likely is that somebody wants to move the thing. Apophis has a dangerous orbit (for Earth); most asteroids have useless orbits. Maybe someone wants Apophis to be our regular Venus-to-Earth shuttle; maybe someone wants Eros in STL4. That's going to shake things up. Do we evacuate?
The obvious worst-case scenario, if a local one, is decompression. Some cars will have EVA suits; all cars have means to patch leaks (GenX may remember Mission Critical; younger Millennials, The Expanse). Most cars, in event they can't be patched, should light up red warnings commanding to GTFO that car and onto some place safer. EVA suitups simply take too long to do the job from there. A professional in EVA will, in EVA's good time, get over there to patch the leak.
A general bad-case scenario is loss of power to the superconductor. The maglev then shuts down. This means the trains slow down, grinding against the outside floor... which floor is set to become the microgravitic ceiling. We'll want auxiliary power-supply but I'm assuming we'll have that; life-support takes a higher priority to spingrav. I'll hope some softlanding strips line the outside "floor", to reduce damage to chassis. The people in the trains have time to secure their belongings before freefall.
Another bad-case is a boulder-blockage. If unscheduled that's a worse-case: the superconductor must activate backwards. This is to grind the cars to a faster halt. There's less warning. In the worst case where the crash cannot be avoided, affected cars must depressurise too, to avoid internal shockwaves and human implosion (so we learn from "Privateer").
As to cleaning up the mess: I've designed for redundancy, so evacuees in need of gravity should switch to the parallel train or maybe even a nearby rubblepile. That'll be the wounded first, like whoever got himself exploded and/or lost eardrums. I suggest also filling the whole track with nonreactive nontoxic gas as long as trains are not running; this probably means nitrogen with a ratio of carbondioxide. Why? So that human mechanics don't need EVA suits - and also, don't worry about fire. Said mechs will of course need goggles (because zero-G dust) and an oxygen-supply.
When it's all fixed, which includes replacing the brakepads: start it up again, and allow the inhabitants back into their appropriate cabins.
