That's the question. Here's some background. We have been a completely virtualized environment for several years. 2 ESXi 5.5 hosts collocated at different data centers connected of course by a site-to-site VPN. The VPN itself is provided by VMs and vCenter runs in a VM at one of the sites as will Update Manager if we go ahead with installing it. If the vCenter and/or VPN VMs are down we have a very cool backup method of accessing and managing ESXi and its console. Some of you reading the rest of this will be tempted to suggest architecting our environment differently but we're very happy with the way it is thank you very much :-) Appreciate all responses but really just answered in this specific question.
The reason we want Update Manager is really just to be able to easily update ESXi in the future without getting into the console and running commands, etc. I realize from documentation and blogs on this subject that ESXi may need to go into maintenance mode and shut down VMs running on it (not a cluster so no migration) at which point ESXi will either lose connection to Update Manager (if the remote host) or shutdown Update Manager (if the local host). So the question is, is the upgrade process managed by Update Manager an atomic operation at this crucial point or a sequence of operations dependent on the continued connectivity and control of Update Manager. Ddoes ESXi then perform the upgrade and reboot independently - which would be great - or is it going to just sit there in maintenance mode waiting for more instructions from the now disconnected/shutdown Update Manager.
Your answers are much appreciated.