The meshichistnicks have been denounced by the mainstream Chabad leaders. They have even taken out a court order to evict the meshichistnicks from 770.
As I understand it, the big battle isn't really over whether or not the Rebbe was the Messiah, but rather over whether or not to PUBLICIZE that the Rebbe was the Messiah. I have yet to see any mainstream Chabad leaders actually denounce the Messianishm, and acknowledge that the Rebbe is: A) dead; and B) not the Messiah.
what the heck is 770