Forgeworld's Sons of Horus Dreadnought is currently sold out, but is coming back. So no need to panic. According to this, other Contemptor Dreadnoughts are most likely going to be re-packed as well.
via Lady Atia on Bolter and Chainsword
http://www.bolterandchainsword.com/topic/312901-soh-contemptor-no-longer-available/?p=4156862
The SoH Contemptor (and i think all others in the future) will just be re-packaged into a clampack - that changes also his code.
He isn't gone and should be available again soon