This came up a few times in random conversation while i was at Counterattack. It wasn't relevant to any of the games I played in so it made no difference to anything, but it surprised me that people did not seem to realise that...
If a broken formation loses an engagement then the entire formation is destroyed.
From here
http://www.tp.net-armageddon.org/tournament-pack/Quote:
If the loser was already broken when it was assaulted then the whole formation is destroyed, and all units in the formation are removed from play as casualties. If the losing formation is not broken then it becomes broken and may withdraw (see 1.13.3).
I'm glad it never came up as I imagine being told that your entire formation is dead when you expected otherwise would be a bit of a shock!