When parts of the PI system are down for maintenance, it might be a good idea to redirect PI Vision users to a webpage to indicate the system is not available due to maintenance.
Digging around, it turns out this is a stock feature of IIS. How to use:
And presto! No more PI Vision.
When done. just rename the app_offline.htm to e.g. app_offline_DISABLED or something similar, and PI Vision should return to normal operation.