A well tool assembly can include a well barrier and a detachable sub connected to the well barrier. The detachable sub can include a sensor data receiver. A method of retrieving sensor data can include positioning a sensor on one side of a well barrier, connecting a detachable sub on an opposite side of the well barrier, the detachable sub including a sensor data receiver configured to receive sensor data from the sensor, and conveying the well barrier, the sensor and the detachable sub together into a well. A system can include a sensor, a detachable sub, and a well barrier positioned between the sensor and the detachable sub, the detachable sub including a sensor data receiver, a passage extending longitudinally through the detachable sub, and a closure that selectively opens and blocks the passage.