People who've never worked with a chassis-based router might find the distinction between control engine and the linecards/fabric hard to understand in an abstract sense.
It's more readily apparent if you've taken an empty Cisco ASR9010 and started from a blank slate configuration with a new pair of RSP440 route/service processors (the control plane) and then incrementally added linecards/interfaces.
Mid to large sized routers are designed in such a way that everything is either N+1 or 1+1 redundant and hot swap, it's like having a four engined airplane you can replace an engine on in mid flight.
It's more readily apparent if you've taken an empty Cisco ASR9010 and started from a blank slate configuration with a new pair of RSP440 route/service processors (the control plane) and then incrementally added linecards/interfaces.
Mid to large sized routers are designed in such a way that everything is either N+1 or 1+1 redundant and hot swap, it's like having a four engined airplane you can replace an engine on in mid flight.