The most that is supposed to happen when LZB goes down, is that the capacity of the line is reduced and there are delays. LZB is not the only train control system.

> ordered to everyone to just restart the march, but the Iryo just couldn't.

Railway protocols operate under the assumption that any train can stop at any time immediately (not even with a braking distance) without the dispatcher noticing. You need to have the information of complete departure of the previous train before allowing the next train to move. If the first train would be able to start, it would still be pure luck if there wouldn't have been a collision.