Well it seems Sierra, Sierra Online, Vivendi Mobile and all of Activisions business will be swept under one division called Activision Publishing, while Blizzard will become a separate, more independant division of Activision Blizzard. It may be that Sierra will be digested into this brand, as I've read that Activision Publishing has always been a monolithic brand name
EDIT: I've read their PDF operation plan extending so far to '09. Sierra is staying, and they intend to green light a lot of products for Sierra in order to improve Sierra's operating income, which apparently for 07 was " -159m" and will seek to create sequels for Sierra's games and will create ''world wide appeal''. Meanwhile, Activision and Blizzard will continue with tried and true formulas.