I don't think it will happen real soon, but SSD will probably replace magnetic HD storage eventually - it's already there in niche usage, just not quite price competative on a per-TB basis yet.
I am not the expert but I don't think HDD's will ever disappear. Not unless they make SSD's as durable as HDD's and cheaper. I probably won't wear out a SSD in my life time but the risk is there. (for now) And there is also HDD's being cheaper than SSD's for per gb/$
Side note: I recently bought a WD 1tb external usb3.0 hdd and it is as fast as (maybe even faster) the first gen SSD's. (tested with "HD tune" software, +200mb r&w/sec) HDD's are still developing technologically.