I think that it would be useful for an Orion server to display an alternate site to Orion when it is offline.
This could be as simple as displaying a page saying the Orion system is down for maintenance with contact details for the administrator potentially.
The caveat that I see with this is that a second IIS site would need to exist on the Orion server and this would need to be brought up using the port mapped for Orion and I assume this would have to be done as part of stopping the Orion services.
Just a thought....
Here's a suggestion. If you have load balancers you can set up a virtual IP arrangement where multiple real ORION web servers sit behind the Load Balancer and all http requests are responded to by the Load Balancer. In fact the Load Balancers can be set up to act as round robin or act as pure fail over.