As long as hard drives can command a solid price/storage lead, they arent going anywhere. For mass storage i will always buy the cheaper/more reliable option. For performance i will buy the most reliable fast option. I have no problem having both a medium size fast drive for my system and performance apps, and a big slow cheap drive for media where it doesnt matter. SSDs would have to cut their price by 90% to change that, Or HDDs would have to increase their performance by a lot to change it.
However they will be pretty much extinct in portable computers. As long as portability isnt in question, they will still rule. If SSDs ever become cheaper/space then spinning disks, then the spinning disks are dead.