I wonder if sacrifice works on CLONE or on magically be-friended enemies.
Anyway - I have two ways how to deal with zounds of dragons:
1. (my favourite) Undead army - Vamps + Ancient Vamps + Ghosts + Cursed Ghosts (when I am warrior - as this works only if your defence / attack is huge, otherwise this is not the best scenario, as normal ghosts and vamps can be slain in first round... when I had 150 ghosts, and the dragons decided to target them, well, I was screwed ... actually the ghosts were
)
2. Demon army (all have 50% fire resistance) + ressurection works on them. The weakest - imps can die very fast, but on the other hand can attack w/o retaliation... so if you manage to take a strategy so the enemy army will not mark them for attacks they are quite handy.