The galaxy-spanning travel and communication nodes, one of which switched off for the first time ever.
Zev explains that tunnel nodes predate their use: long before The Plenty worked out how to open them for communication and travel, the nodes were simply visible — a map of the stars pointing the way to every seeded world. They are permanent fixtures of the galactic order. Systems have been watched going nova and their nodes stayed lit; nobody even believed a tunnel strand could disappear.
The node serving the Aryl System went offline in the exact nanosecond orcs triggered The Failsafe, and with it gone, rescue is impossible — even the antiquated Borant Gate System will not reach a system whose node is dark. Zev is emphatic that this has never occurred in recorded history and that nobody knows what it means.
Fixed points on the star map, visible to civilizations long before they could be used for travel.
The backbone of galactic travel and communication, now proven to be something that can be switched off.