I don’t think it’s an issue in Home Assistant, rather a (lack of) feature of the IKEA bulbs themselves.
The gateway doesn’t update the status for the non-reachable bulbs.
if you try to turn_off a tradfri light with home assistant after cutting it from the power supply, the ikea gateway updates the lights status as unavailable and homeassistant shows it as such.
you just have to find a way, or rather a sensor, that tells you that the power supply was cut. in our bathroom i’m doing this with a light sensor. so if the bathroom turns dark (or rather below a certain brightness level)), i let HA turn off both tradfris. this updates their status to unavailable if the light is cut from power (or just turns it off, if it still has power).
another workaround would be to turn off the tradfris if there’s no motion for a couple minutes. this would give you the unavailable status with a bit of lag.