Strange times we live and fly in.
Aircraft are mandated to have duplicated / standby systems or manual reversion.
As pilots we have to be able to fly manually if the autopilot fails.
We also have to be able to revert to other means of getting from A to B and landing if our primary navigation aids fail, even stop watch and compass dead reckoning.
Any failure in an aircraft (and like anything mechanical, electrical or electronic things do fail) is likely to affect just that one aircraft.
Yet a critical ATC main system, which if it does fail, affects all aircraft under its supervision, doesn't have any manual backup?
Crazy.