If you buy a new hard disk and install it the keyboard won't even boot (start), because there is no operative system on the drive itself (the same thing that would happen with your PC if you don't install Windows first). Your only chance in case of hard disk failure is to send the keyboard back to the assistance and have the defect corrected (usually there is a problem in the connection between controller and hard disk). In the worst case they will have to install a new hard disk and copy everything (OS, sounds, audio styles, etc) again in it. To avoid losing all your data (new or modified styles, user registrations, etc) is advisable from time to time to make a backup of all the files on your computer (using the USB cable).
Korg Kronos 61 and PA3X-Pro76, Roland G-70, BK7-m and Integra 7, Casio PX-5S, Fender Stratocaster with Fralin pickups, Fender Stratocaster with Kinman pickups, vintage Gibson SG standard.