The GE ports cannot fail open on their own. You must purchase an optical bypass kit for each port pair you wish to fail open.
If a Sensor is restarted, hangs, or fails to come up after being turned on, the optical bypass kit takes over and ensures the link remains active. When configured as a HA pair, this logic still applies, except in the case in which the Sensor port actually fails. In this case, the bypass kit does not change to bypass mode. Instead, the port pair fails closed and the redundant link takes over.
The details of optical bypass kits are beyond the scope of this document. Refer to Trellix Intrusion Prevention System Gigabit Optical Fail-Open Bypass Kit Guide, which accompanies the Optical Fail-Open kit.