A HICAS lock bar is a steel bar with mounts on it that bolts inplace of the rear steering rack and holds the rear wheels completely rigid, therefore locking out the HICAS.
I drove without HICAS on for ages when my car had no speedo, the only thing that will happen is that your steering will most likely be heavy and the rear may feel a little "unsettled" as the rear wheels wont be steering but they may move slightly under load.
I dont think it will do any damage driving without it as mine is working again now after being disabled for a few months.