Heroes and coexistence Battles

By tech7, in Horus Heresy

I have a question.

The rulebook states that a Hero causes a coexistence battle, even if unsupported, correct ?

However, the battle ends if there are no units (Heroes are not units, there is even an example in the rulebook) .

Now what happen in a coexistence battle with a Hero.

1 - No iteration is fought since the battle ends immediately

2 - 1 iteration is fought

3 - the battle goes on until one of the other ends of battle conditions is triggered ?