@dongjh, from the vSAN perspective, nothing should happen - vSAN nodes have no reliance on DNS for node to node communication and the cluster should stay fully-formed and thus nothing inaccessible.
If you have some VMs or applications that require DNS to function then that might be a different story, but then that would be the same regardless of running on vSAN or VMFS or any other storage platform.
Thank you for your reply.