Just curious, ....or when do characters leave units?

He explicitly loses ItP while in a unit which isn't ItP, as per the Character Psychology rules.

Psychology Section: Frenzied troops are ITP

Character Section: "A Character that is immune to psych and joins a unit loses it as long as he is with them. If the character leaves the unit by declaring a charge, he automatically regains his Immunity (including during that charge)"

I interpret it as this: For the purposes of this, when the character is in the unit, he is treated as part of the unit. That said I would be curious as to whether a khorne Wargor in a herd, when the herd fails a fear test during being charged would be immune or hit on 6's. To me it seems like it should still be immune, but per the rules that may not be true.

That said the immunity is always there, but because it's the unit involved, not the character, that's where we sit on that. When its solely the character involved it becomes painfully obvious that this isn't a problem because he is the one charging, not the unit.

Wow....next time I need to check a page again before citing it. You're right that he regains it by declaring the charge. Good catch. No terror test for the Wargor.

As for when the herd fails a fear test, the character lost ItP, so he's hitting on 6's.

In our case a character DOES NOT declare a charge, thus not leaving a unit. The unit declares (and fails) charge, dragging away the character, who haven't left it.