Not steer-by-"wire" exactly but in the 1970s and 1980s Citroën had cars with "DIRAVI" steering. In normal operation there was no direct mechanical link between the steering wheel and road wheels. The whole thing was a big hydraulic servo, with "resistance" applied to the steering wheel using a heart-shaped cam, a big spring, and a small hydraulic piston that had progressively more pressure behind it based on road speed.
If you let the steering wheel go it would spring back to the middle even with the car at a standstill because of the resistance cam.
If it lost hydraulic pressure while you were driving there was still generally enough in the system to allow you to pull over safely, and you could drive for much longer distances if you could cope with about a quarter of a turn of "play" in the steering wheel. With no pressure at all, turning the steering wheel would move the shuttle valve in the steering controller until it bottomed out and then the linkage would just turn the pinion on the steering rack, which was normally used for servo feedback. Uncomfortable, but acceptable for "get off the road" situations.
The hydraulic system also worked the self-levelling suspension, the fully-powered braking system (similar to the WABCO systems on a lot of more modern vehicles), and on some manual gearbox models the clutch.
Not really "drive by wire", because it's not electronic, but it really is a system where the steering rack could be fully decoupled from the steering wheel.
