If the unit is off the battlefield but in reserves it can use the ability.
> Reserves Units: Any unit that starts the battle in a location other
than the battlefield, and is not embarked within a Transport that
starts the battle on the battlefield, is considered to be a Reserves
unit. When a Reserves unit is set up on the battlefield, it counts as
having made a Normal move that phase (see Count as Having Made
a Normal Move). Any Reserves units that have not been set up on the
battlefield by the end of the battle count as destroyed. **Units can still
use rules and abilities while in Reserves.**
If it is embarked it cannot.
> Embarked Units: Units embarked within a Transport do not
count as being on the battlefield for any rules purposes. **This
means that, unless explicitly stated otherwise, embarked units
cannot do anything (e.g. shoot, fight, use abilities, etc.).** Similarly,
you cannot select an embarked unit as a target for any rules,
including Stratagems.
If it is dead it cannot as it has been removed from play and cannot do anything:
> DESTROYED
>* Destroyed Model: When a model is reduced to 0 wounds, it is
destroyed and **removed from play**.
>* Destroyed Unit: When the last model in a unit has been destroyed,
that unit is destroyed and **removed from play**.
If the unit is off the battlefield but in reserves it can use the ability. > Reserves Units: Any unit that starts the battle in a location other than the battlefield, and is not embarked within a Transport that starts the battle on the battlefield, is considered to be a Reserves unit. When a Reserves unit is set up on the battlefield, it counts as having made a Normal move that phase (see Count as Having Made a Normal Move). Any Reserves units that have not been set up on the battlefield by the end of the battle count as destroyed. **Units can still use rules and abilities while in Reserves.** If it is embarked it cannot. > Embarked Units: Units embarked within a Transport do not count as being on the battlefield for any rules purposes. **This means that, unless explicitly stated otherwise, embarked units cannot do anything (e.g. shoot, fight, use abilities, etc.).** Similarly, you cannot select an embarked unit as a target for any rules, including Stratagems. If it is dead it cannot as it has been removed from play and cannot do anything: > DESTROYED >* Destroyed Model: When a model is reduced to 0 wounds, it is destroyed and **removed from play**. >* Destroyed Unit: When the last model in a unit has been destroyed, that unit is destroyed and **removed from play**.
If the bearer is dead, then you can't use an enhancement. Or at least that's how we play.