Type 1 and type 2
Given that VirtualBox is the only type 2 hypervisor in Oracles "smorgasbord" of hypervisors, I wold give it a fair chance to survive.
The big question is what type 1 hypervisor they will keep around, but as both VI and xVM Server is Xen based I wold guess that they rather continue with a Xen based hypervisor than jump on the fairly unproven KVM train. Secondly by potential merge the eng. resources from VI and Suns xVM team they will have a substantial expertise in Xen based hypervisors.