I’ve no idea - haven’t you watched it? If it doesn’t actually change then of course your rule will not trigger. It could take forever, see below.
Well, yes.
An openHAB MQTT Thing just sits there waiting for incoming messages from the broker. It has absolutely no way tell if any remote device even exists.
The broker is the one with the direct connection that could find out, but the broker doesn’t know if anyone wants to hear about it.
There’s a special mechanism in MQTT called “LWT”. The remote device has to initiates this when it signs on to the broker. “Hi, can you tell people if I die”. That means your Garage Opener needs to support and be configured with a LWT.
Then you need to configure the openHAB Thing to subscribe for that LWT message. Some about that here
I do not think any of this works at openHAB version 2.5.0 and you should move up to 2.5.11
There might be another approach -does your garage thingy send regular status updates? We might be able to check for a missed report.