As things currently stand, the Gladys interface has no notion of a « connection » with devices, it just sees when the last value report occurred. For a temperature sensor that sends a value every hour, for example, you can deduce after 12 hours that there is an issue. For a door open sensor, after 3 days that doesn’t mean anything — the sensor may be fully functional, the door just hasn’t been touched in 3 days…
Edit: There is already a feature request for that, feel free to vote for it!