"What if the Enterprise-D failed to stop the Borg in BOBW?"
And do you think the Vulcans would have abandoned Vulcan under the pretext of:
"Earth and Starfleet Headquarters have been assimilated. Including several Vulcans. There is no plan we can come up with that the Borg cannot anticipate. Logically their next target will be Vulcan. The logical course of action is to deny the Borg any more drones and to abandon Vulcan."