I’m not an expert on hard drive but here is what I think, It is possible that hard drive will disappear but I think that the Flash hard drive will be use more for getting faster cash I/O than replacing hard drive. Look a the new SUN NAS. they are using 10k RPM SATA drive disk with flash drive and the seem to have the fastest NAS of the industries. But technology wise I would say get ride of all mechanics and yesonly electronics part. so you illuminate a point of failure. The day we will see flash drive of TB is probably not far ahead but to replace hard drive that is something else.
Last week I had a chat with one of the main storage vendor and they are going fast forward on flash drive. It seam that hard disk drive will extinct and sooner that I thought.
Here is an article that ask good questions when a company think on changing to flash SSD drive