[Fantomen]

IIRC:

Every turn your unit is in the void it may be attacked. If it loses the battle it is killed, otherwise it stays in the void. There is a small chance every turn for your unit to return from the void, it is however totally random and may never happen. Units returning from the void can be a bit insane from the experience.

And there is absolutely nothing you can do about it.

Someone correct me if I'm wrong.