The https monitor will alert when the certificate expires because it can not create a secure conection to a server. We found this out the hard way when a certificate expired which we forgot about.
We are using v8.5, but I assume v9.x has the same functionality.
The ability to monitor the expiration date on an SSL Certificate is currently a feature request which is being considered for a future version of ipMonitor. If you wish to be notified when this gets added, simply open a case using the following form and we can then link the case to the feature request: