What's the most efficient setup for minimizing downtime for system maintenance or server upgrade with Hyper-V and Windows Server 2012?
Live migration only takes care of updating Host, how to address updating VM?
hosts are easy because of live migration. you got that covered.
if the services on your guests don't support high availability or load balancing then you can have two fully configured guests, each with two network interfaces. one of the network interfaces is configured with a unique management ip address. the other nic on each is configured with the same ip for exposing the services. one of the guests should have this nic disabled. you can update the guest with the disabled nic. when you're done, disable the nic on the live guest and enable the nic on the updated guest. do it quick enough and the downtime should be minimal.