If you download and install the content using the optional updates (without purchasing the content), the next time the site is brought down for maintenance you could use the Test Drive site (https://testdrive.iracing.com/ or access by opening the Beta UI during maintenance) which is only online during times of maintenance on the main service.

As long as the current version of the content was installed at the time the service was brought down, you would be able to use it in the Test Drive service.

Downtime announcements are posted in the forums as well as on Twitter (@iRacingSupport)