When the HCU Unit has failed the braking system in theory reverts bake to standard braking, but I have see isolated issues where the ABS has an unexpected application and prevents the vehicle from properly coming to a stop ( false activation ), and that is not a comfortable feeling. It may be drivable but braking can be an issue. Depending on if you need the HCU and the ECU it can get very pricey. The option here is a used part , go to Car-Part .com shop local or regional for a used part. I have included screen captures of the site.