You should still have some power steering, it will just be a lot stiffer than usual at low speeds, this is normally due to dry solder joints in the HICAS ecu in the boot. After a while, it heats up and something expands on the circuit board, causing a short, or an open, which isn't normal. This seems to make the ECU think that it is going at a higher speed than it is, so the power steering stiffens up for stability.
There are numerous solutions to the problem because there are numerous causes to the problem. New sensor would only fix it for someone who has a dodgy sensor, obviously.
I'd recommend a lock bar personally, fk hicas right off...
Mine would do as you described (Series 2 though) if I went for a long drive (like 40 minutes home from work, stop at the servo, then start it again) More commonly happened in Summer.